MG Im5 vs Mercedes-Benz SL63

What's the difference?

The MG IM5 Performance is fast, comfortable, quiet and super refined. Putting some minor spec and active safety niggles to one side, it offers the features, tech and price to match it with its well-credentialled and already popular mid-size EV sedan competitors. Is there room for one more? We think there should be.

The new Mercedes-AMG SL63 4Matic+ is guaranteed to turn heads for decades to come. But there’s enormous design and engineering substance underpinning this car’s undoubted good looks. Stunning performance, superb dynamics and top-shelf safety make this a powerhouse GT to be reckoned with.

Note: CarsGuide attended this event as a guest of the manufacturer, with accommodation and meals provided.

Playing spot the straight line on the outside of the MG IM5 is like an automotive design version of Where’s Wally? There aren’t many, in the midst of an unrelentingly curvaceous exterior treatment.

At close to five metres long and two metres wide the IM5 is appreciably longer (+211mm), a little wider (+27mm) and a bit taller (+33mm) than a Tesla Model 3. Think BMW 5 Series in terms of overall size.

And the soft-form shape is functional; the swoopy liftback boasting an ultra-slick 0.24 drag coefficient.

That said, I’m not convinced by the ‘Periscopic’ cameras informing the driver assistance systems from the front guards. They scream tacked-on afterthought. But a touch-only initial opening function for the flush door handles is cool and makes life easier.

The curves continue inside with soft-padded surfaces around the dash and doors, but the straight edge obviously came out for the 10.5-inch central media screen and vast 26.3-inch upper display. There are next to no buttons; even exterior mirror adjustment is directed from the screen to a multi-function steering wheel control.

System software (powered by a Qualcomm ‘Snapdragon’ chip) is lightning fast with a two-finger up and down swipe shortcut function on the central screen for ventilation and other functions.

The interior is light and bright thanks to the enormous panoramic sunroof. It’s been fine in cooler winter conditions during this test but it could be interesting to revisit in the heat of an Aussie summer

There are two interior colour schemes available - the ‘Highland Grey’ of our test car or ‘Dover Beige’ for those brave enough to live life with the threat of scuff marks on your shiny new car’s glamorous but vulnerably light interior.

Rather than a strict two-seater, this time around the SL adds the flexibility of ‘+2’ rear seating while the previous 'Vario’ folding hardtop has been binned, the new car returning to a traditional, electrically-folding and weight-saving (-21kg) soft top. 

Mercedes-Benz design chief Gorden Wagener started the new model’s development from a ‘clean sheet’ and Mercedes-AMG says “not a single component comes from the predecessor SL, or any other model such as the AMG GT Roadsters”. 

Always a subjective call, but I think this car’s proportions are just about perfect. The lengthy bonnet with its twin longitudinal ‘Power Domes’, raked windscreen and fat haunches create a wide stance and presence that’s almost impossible to ignore.

Aggression, as with the sinister headlights and 21-inch rims, is subtly combined with soft curves along the flanks and around the rear. Note the seamless door handles.

And it’s not all about aesthetics. Active aero has been integrated into the front apron and retractable rear spoiler. Plus the ‘Z-fold’ roof design does away with the need for a separate cover.

The interior is sub-zero cool with slick screens, an 11.9-inch display covering multimedia and a 12.3-inch unit for instrumentation ahead of the driver, being particular highlights.

Turbine-style air-vents at the leading edge of the split-level dash and alloy trim elements are a tip-of-the-hat to SLs past and the deft mix of large flat surfaces with complex curves oozes design confidence.

There’s plenty of breathing room up front and in terms of storage one of the first things worth calling out are the long but relatively narrow door bins. No good for anything above unusually slender bottles, even if they’re lying down.

No conventional glove box in the dash, but there is a large lidded box (cooled and heated) between the seats that doubles as a centre armrest. It’s supplemented by a big stowage area underneath the flying buttress style centre console.  

There are two cupholders in the centre console as well as a wireless device charging pad in front of them with a vaguely phone-shaped oddments bin alongside it.  

Move to the rear and the IM5’s 75mm wheelbase advantage over the Tesla Model 3 is clear. Heaps of knee and headroom for me at 183cm sitting behind the driver’s seat set to my position. 

But… the seat sits low which pushes your knees up into the air to the point where my thighs are not contacting the seat cushion. Even though the rear seat reclines to a certain degree it’s a problem compounded by a chronic lack of room for your toes under the front seat. Awkward.

There are map pockets in the front seatbacks, modest bins in the doors and a fold-down centre armrest with two cupholders. Adjustable ventilation in the rear of the front centre console always makes life in the rear seat more pleasant.

The car also houses ‘Strong Magnets’ at various points around the cabin and boot, with a configurable adapter able to lock a phone or tablet into place for the entertainment of, in our case, back seaters. 

Speaking of devices for entertainment, there are two USB-C sockets and a 12-volt outlet in the front and another USB-C and 12V in the back, so charging isn’t an issue. 

The IM5 is a liftback so the boot aperture is generous and a capacity of 457 litres with the rear seats up is decent for a car of this size, although that’s less than the Tesla Model 3 (594L) which has an additional well under the floor. 

Still, enough room for the largest (124L) and smallest (36L) suitcases from the CarsGuide three-piece luggage set with some room to spare.

The power tailgate can be operated hands-free via the key or an always welcome under bumper kick function.

Volume expands to 1290 litres with the rear seats folded and there’s a modest 18-litre ‘frunk’ under the bonnet.

The bad news is a repair-inflator kit rather than a physical spare wheel, but the better news is the IM5 Performance can tow a 1500kg braked trailer (750kg unbraked).

The IM range also features the ‘MG iSmart’ app allowing remote control of various functions including charging, checking vehicle location and route planning. 

In the context of a high-performance GT, practicality is pretty impressive.

At just over 4.7m long the SL is a sizeable machine and much of its lengthy (2700mm) wheelbase is devoted to making the driver and front passenger comfortable.

There’s plenty of space for that pairing and just enough storage to cope with the ‘things’ they’ll typically bring with them.

Door pockets offer enough room for a few odds and ends, although you’ll struggle with even a medium-size bottle unless you’re willing to lay it down horizontally along the top of the aperture.

A handy lidded bin between the front seats doubles as a centre armrest, there are two cupholders under a sliding lid in the centre console and the glove box is a decent size. 

Power and connectivity options run to four USB-C ports, a 12-volt socket and the wireless device charging pad.

Then there are the rear ‘+2’ seats, and Mercedes makes no bones about the fact they’re intended for occasional use only, even suggesting a 1.5m occupant height limit.

And there’s no doubt they offer a handy emergency seat or a fun kids’ zone. Just ask a Porsche 911 Carrera owner how much this kind of seating arrangement increases a sports car’s flexibility.

At 183cm I gave the back seat a crack, which meant sliding the front (passenger) seat way forward with the backrest close to upright. But I squeezed in, and there was just enough legroom for a person in front at the same time. 

With the roof in place there’s the added pleasure of cranking your head over to around 45 degrees. But it’s do-able! 

No storage, adjustable ventilation, or power back there. But that’s fair enough, especially given there are USBs available in the front centre storage box.

Boot volume is 240 litres with the roof up and 213 litres with it folded, which is enough for some light luggage, and not too shabby when you think a Toyota Corolla hatch offers up just 217 litres (with all seats up).

There’s a 12V socket in there, but don’t bother looking for a spare, in the event of a flat your only option is a repair/inflator kit.

Priced at $373,370, before on-road costs, the new SL63 4Matic+ will be battling top-shelf performance soft tops including (in ascending dollar order) BMW’s M850i xDrive Convertible ($307,100), the Porsche 911 Carrera GTS Cabriolet ($386,900) and even exotics like the Lamborghini Huracan RWD Evo Spyder ($422,606). 

Value for money is a relative concept in this part of the market, although equipment highlights include a head-up display (with augmented reality nav), 11-speaker, 650-watt Burmester surround sound audio, ambient lighting (choice of 64 colours), hectares of Nappa leather trim, dual-zone climate control, an 11.9-inch central multimedia screen (running Merc’s latest ‘MBUX’ software), 12.3-inch configurable digital instrument display and 21-inch forged alloy rims.

There’s also the ‘Digital Light System’ built around three high-power LEDs in each headlight, refracted and directed through 1.3 million ‘micro-mirrors’ to create a combined resolution of 2.6 million pixels.

The ‘Neck Scarf’ function is added to the top of the front seats to keep your neck and the back of your head warm as the temperature drops, the heated, ventilated and massaging front seats feature eight-way electric adjustment and three memories, there’s a heated steering wheel, Android Auto and Apple CarPlay connectivity, wireless device charging and more.

Worth noting the big 21-inch rims in a ‘10-twin-spoke’ design are standard issue with an alternate ‘multi-spoke’ pattern available as a no-cost option. 

But if all that’s not enough you can opt for ‘AMG Performance seats’ ($2490) which grip you even more securely but delete the massage function.

Or there’s the ‘AMG Night Package’ ($6990) which adds wheels in matt black (with “high-sheen finish rim flange”), darkened head- and tail-lights, an aero package, black badging, black radiator fins and interior trim elements in black chrome.

Then you can go the whole hog with the ‘AMG Carbon Fibre Package’ ($11,990) which brings the wheels in matt black, exterior carbon elements, carbon mirrors, carbon interior trim and a steering wheel in a combination carbon-fibre and Dinamica (synthetic microsuede).

The MG IM5 Performance is powered by an electric motor on each axle - the rear (372kW/500Nm) more powerful than the front (200kW/300Nm), for overall outputs of 572kW (that’s close to 770hp) and 802Nm of pulling power.

The official term for that amount of grunt is… a lot. And we’ll get to what it means on the road in the Driving section shortly.

This new ‘4Matic’ all-wheel-drive SL63 features AMG’s (M177) 4.0-litre twin-turbo V8, superseding the previous rear-wheel-drive SL’s similarly configured 5.5-litre unit.

Hand built by one AMG technician from start to finish, it produces 430kW (around 580hp) from 5500-6500rpm and 800Nm across a broad plateau from 2500-5000rpm.

It’s something of a mechanical masterpiece, and the previous seven-speed auto transmission, driving the rear wheels only, has been replaced by a nine-speed dual-clutch auto (with wet multi-disc start-off clutch) sending drive to all four wheels via Merc’s ‘4Matic’ AWD system.

The MG IM5 Performance features an 800-volt electrical architecture which means the 100kWh NCM battery can accept a DC peak charge of close to 400kW.

Only snag is the highest you’ll currently find in Australia is 350kW. But even at that rate you’ll still be looking at a 30-80 per cent charge in just over 15 minutes. Maximum AC charge rate is 11kW.

Claimed range is 575km (WLTP) which is less than the Tesla Model 3 Dual Motor AWD at 629km.

Over a week of city, suburban and some freeway running we saw average energy use of 20.6kWh/100km which is on the high side for an EV of this size but maybe not for one with this kind of performance potential. 

Mercedes-AMG’s official fuel economy number for the SL63 on the combined (WLTP) cycle is 13.9L/100km, the 4.0-litre twin-turbo V8 emitting 319g/km of CO2 in the process.

On the roughly 300km launch program we covered urban, B-road and some freeway running, returning an (indicated) average of 17.5L/100km. And that reflects some enthusiastic driving along the way.

The fuel tank requires 70 litres of 98 RON premium unleaded to fill it which translates to a theoretical range of around 500km, dropping to 400km using our real-world number.

First things first, the IM5 Performance is supercar fast. This 2.3-tonne five-seater blazes from 0-100km/h 3.2 seconds and with its dual motors combining to produce 572kW/802Nm, eye-widening performance always resides underneath your right foot.

But it’s not all about straight line speed. Ride comfort is excellent. Underpinned by an all-new platform, the IM5’s suspension is by double wishbones at the front and multi-links at the rear. But the key to its bump and rut smoothing ability is air suspension and ‘continuous control’ active damping.

Fold in double-glazing on the full-length glass roof and side windows, as well as active noise cancellation and you have a serene interior environment at any speed. Also worth noting the front seats are great; as grippy as they are comfortable.

Not only that, despite its relative heft, this mid-sizer steers well, too. Not the last word in road feel but it points accurately and the standard rear steering helps with prompt (but never jerky) cornering turn-in. Flick to ‘Sport’ mode and the IM5 is up for some enthusiastic running.

The rear wheels can turn up to 12 degrees in the opposite direction to the fronts at slow speed, which makes for a usefully tight 10-metre turning circle. But above that, at lesser angles, it adds extra stability and decisiveness in the way the car steers through even tight, twisty sections.

Rubber is top-shelf Pirelli P Zeros on 20-inch alloys (245/40 fr - 275/35 rr) and it grips hard, especially in the wet weather over much of the test period. Braking is solid, as it needs to be, with ventilated discs all around and four-piston callipers at the front. 

No adjustable regen braking but you can feel the ‘Cooperative Regenerative Brake System’ (CRBS) doing its thing when you lift off the accelerator. 

The physical rear view is modest thanks to the slope of the back window reducing its functional area for the driver to that of a 1950s VW Beetle. Even the interior rear-view mirror is tiny and folds up into a recess in the headliner if you’d prefer life without it.

But that’s where a rear camera view popping up on the upper screen display (accessed via the right-hand steering wheel click control) comes in handy. Side camera views are also available as is a 360-degree overhead view, which makes parking straightforward.

If you need more parking help there are various self-parking modes including a nifty ‘Curbside’ function that will realign the car hands-free if you’re parallel parked too far out from the kerb.

In a similar vein, a ‘Rainy Night’ mode projects left and right rear views onto the main screen using AI to enhance clarity and highlight pedestrians and cars.

Overall the ADAS (Advanced Driver Assistance Systems) are relatively unobtrusive but we found ourselves switching off the incessant overspeed chime that sounds for 10 seconds if you creep over the indicated speed limit, even when the system has misfired on the correct speed. For example, 40km/h school zones on a Sunday.

The over-zealous driver distraction warning also occasionally issued a visual and audible slap on the wrist when I was looking straight ahead. Tellingly, there’s a specific quick screen for turning both these functions off, but it kinda defeats the purpose of having them in the first place.

We also found the adaptive cruise control to be hesitant in multi-lane environments, reducing speed occasionally because the system seemingly believed a car was set to merge, when it wasn’t.

I recall driving the AMG SL65 around the backroads of Tassie a few years ago and that twin-turbo V12 monster famously packed 1000Nm of torque, while this car ‘only’ has 800.

But there comes a point where enough is enough… and this is enough!

With maximum torque available from 2500-5000rpm and peak power (430kW) on call from 5500-6500rpm there’s always stupendous acceleration available with a squeeze of your right foot.

Claimed 0-100km/h time is supercar fast at 3.6 seconds, while top speed is a toupe-troubling 315 km/h. And that’s electronically limited!

A typically ferocious engine noise and howling exhaust note accompany rapid progress and shifts from the nine-speed dual-clutch transmission are quick and positive, not to mention especially enjoyable using the steering wheel-mounted paddles.

There are six ‘AMG Dynamic Select’ drive programs from Comfort through to Race, the latter including a Drift Mode, which we didn’t experiment with. Nor did we dip into the ‘AMG Track Pace’ system for circuit-focused mapping and timing

However, far from drifting, the grippy Michelin Pilot Sport 4S rubber (275/35 fr - 305/30 rr) plants the car securely with the all-wheel-drive system and electronic locking rear diff playing their part.

I found the perfect set-up was in the ‘Individual’ mode with the engine, transmission and steering in racier settings and the suspension in ‘Comfort’. The adaptive damping in this configuration mixes smooth ride compliance with sharp dynamic response.

The car’s aluminium space frame chassis is part of a body structure mixing aluminium, magnesium, fibre composites and various strength steels.

Torsional rigidity is claimed to have been improved by 18 per cent and despite the lack of a roof the SL feels tight and solid.

Suspension is by alloy double wishbones front and rear with adaptive damping and active hydraulic anti-roll stabilisation standard (so, no physical anti-roll bars).

At the same time the 4Matic AWD system is able to vary torque distribution up to 100 per cent to the front or rear axle depending on where drive can be put to best use.

The speed sensitive, variable ratio, electronically controlled steering is accurate and turns in beautifully with good road feel. No doubt assisted by electric rear steering able to adjust the angle of the rear tyres by up to 2.5 degrees.

All this adds up to a hugely impressive package that, despite its 1970kg kerb weight, feels agile, athletic and able to attack corners like an overgrown hot hatch, putting its power down with unwavering authority.   

While indecently fast the SL63 can also stop rapidly with the AMG high-performance braking system standard. 

Huge composite ventilated and cross-drilled discs (390mm fr - 360mm rr) are clamped by six-piston fixed alloy calipers at the front and single-piston units at the rear. They wash off speed calmly and consistently with perfect pedal feel.

Even at highway speeds, particularly with the windows up, normal conversation is easy with the roof down. But if you need to raise (or lower) it, the operation takes 15 seconds and is possible up to 60km/h. 

Under the heading of miscellaneous observations, the turning circle is a not insubstantial 12.8m, so beware in the car park.

A front axle lift function is a welcome standard feature, raising the car’s nose 30mm with the press of a button. And lift locations are stored in GPS data, so the car will subsequently remember to lift itself at the same place, even if you don’t! 

Heating and cooling for the front seats combined with the heated steering wheel and Air Scarf neck warming makes winter top-down driving a pleasure.

The digital instrument display is not only crystal clear, it can be changed through multiple configurations, including a tunnel-like graphic for engine revs as well as specific readouts for speed, g-force, the lot.

At the same time, the central media screen’s angle can be adjusted to better cope with reflections and the windscreen wiper system Merc calls ‘Magic Vision Control’ channels fluid along the wiper arms onto the rubbers, which isn’t new, but works spectacularly well here.  

No independent ANCAP safety assessment at this stage but the SL63 is fitted with the ‘Driving Assistance Package Plus’ which includes a heap of active (crash-avoidance) tech including AEB (with pedestrian detection), active cruise control, lane keeping assist, lane change assist, traffic sign assist, ‘Active Traffic-assist’ and ‘Active Steering Assist’. 

There’s also tyre pressure monitoring and the ‘Active Parking Assist with Parktronic’ self-parking system supported by a 360-degree camera view and multiple sensors. 

If a crash is unavoidable the airbag count runs to eight, including side bags for rear occupants. There are ISOFIX anchor points for child seats or baby capsules in the two rear and front passenger seat positions. And an active bonnet is designed to reduce injuries in the case of a pedestrian impact.

The MG IM5 Performance is covered by a seven-year/unlimited km warranty, which is a plus, but the catch is it’s conditional on authorised dealer servicing. Go elsewhere and the term drops to a more common five years/unlimited km. The drive battery is covered for eight years/160,000km, which is the norm in the Aussie market

Servicing is required every 12 months or 20,000km with charges averaging $586 per workshop visit for the first five years, which is on the high side for an EV, even at this price point, the average bumped up by a more than $1400 doozy at year four.

MG IM models are sold (with service available) through all of MG’s 100-plus dealerships across the country, so no concerns there.

The SL63 4Matic+ will be covered by Mercedes-AMG’s five-year/unlimited km warranty, with roadside and accident assistance included for the duration, both of which are expected in this category. 

Maintenance intervals are 12 months/20,000km, and a fixed-price service plan lists an average of $1583 for each of the first three visits to the workshop. Not exactly small change, but not unheard of in this part of the market.