Mercedes-Benz AMG GT vs Mercedes-Benz SL-Class

What's the difference?

The GT63 4Matic+ is a breathtaking example of everything that Mercedes-Benz and AMG are.

Ferociously fast, incredibly agile and superbly sophisticated, it should be on anybody’s shortlist, if that also includes a Porsche, Aston Martin, Maserati or even a Lamborghini. And it’s definitely much more than yesterday’s SLC ever was – for similar money in today’s terms, as it turns out.

But, around Tasmania’s glorious roads at least, the Mercedes-AMG lacks the ride comfort and road noise isolation to be a fully-rounded-out GT, and that’s a disappointment for a brand with such formidable history in making such cars.

The SL's overall score is somewhat skewed by everyday concerns, and rules are rules - an average punter will find the price of this car somewhat confusing and the devil-may-care attitude to fuel consumption bewildering.

If neither of these things are a problem, then the SL63 makes plenty of - well, not sense, because it's not a particularly clever or considered car - but it fills a niche that not so long ago we all thought would go the way of the dodo.

The fact it sells so few examples is betrayed by some of the cabin amenities and the fact that Mercedes hasn't put much effort into reducing the car's weight to improve its consumption or sharpen up the handling.

The fact it still exists at all is pretty damn cool, though, and for certain people an SL63 purchase is the culmination of a lot of hard work.

If it is your dream car, the SL63 won't disappoint. Everyone who rode with me said it was mightily impressive, but you've got to really want it. When you're not far off buying a Ferrari California T or Aston Martin V12 Vantage S for the money, you'll need a real yearning for the three-pointed star to go this way. And if you do, good luck to you - you've probably worked quite hard to get here.

This is still clearly a Mercedes AMG GT coupe, like the 2014 C190 original, but a ground-up redesign sees it subtly yet significantly altered.

Some 270kg heavier than before, the larger-in-every-dimension body combines aluminium, steel, magnesium and fibre composite materials for improved rigidity and a lower centre of gravity. Length (4729mm) and wheelbase (2700mm) have been stretched by 177mm and 70mm respectively. Width (1984mm) and height (1352mm) are also up.

The nose treatment is similar to before, especially with the bulgy bonnet and signature vertical slatted grille fitted. These, combined with the LED digital headlight shape effect, is reminiscent of, but far-better executed than, the goofy-looking MG5’s face.

Underneath, it's an all-new platform shared with the SL, with the rear transaxle of the old car replaced by a permanent AWD system, leading from 46:54 front/rear weight distribution to 50:50 as a result.

That aggressive, exaggerated cab-backward/ultra-long bonnet silhouette that visually connected it with the SLS gives way to more-conventional and practical coupe proportions that is striking if not especially original, since they do look quite 911-esque. Along with the longer wheelbase and wider tracks, the result allows for two small rear seats to be fitted, while liftback cargo access remains.

Similarly, in the name of way-more usable interior packaging, Mercedes-AMG says it pushed the driving position nearly 180mm forward compared to the previous GT. Let’s see what that all looks like inside.

The SL has always been completely unapologetic about its size and seems to be designed to accentuate rather than hide its length and width. The long bonnet screams power and prestige, and get out of my way, and is reminiscent of the little-loved McLaren SLR project of some years ago.

The size of the Mercedes logo on the huge front grille leaves you in little doubt about the brand of car that’s about to pass you at speed and some might say (okay, I would) that its large surface area is a little vulgar.

Like the SLR, the design doesn't seem to have a particularly cohesive strategy, with a number of Mercedes elements from around the traps that climb over each other. Roof up it looks awkward because of the gigantic posterior while with the roof down it looks overly long and, again, tail-heavy.

Folding hardtops are notoriously cumbersome and need a lot of room to hide them, but the silent operation is something to behold.

Elements that are worth deleting if possible are the dodgy 'Biturbo' badges. It's that kind of bling that gets people raising their little finger at you.

The first impression inside is that of space, despite the falling roofline and coupe-like upsweep of the side windows and you look back. While, again, similar to a 911s, a kink at the door gives the GT a unique character.

Even larger people will appreciate the generous amounts of room up front, with space to stretch, sat in sumptuously comfy bucket seats. Note that the standard ones are better than the racier but firmer Sports versions.

The driving position is perfect, ahead of a dashboard that is very typical modern Mercedes in appearance and layout.

To that end, the tablet-style integrated touchscreen (11.9 inches) is clear, fast and intuitive once time is taken to learn it. And points are also won for the multi-configurable electronic instrumentation, that allows for a variety of screens, including track, classic and minimalist views.

The trademark turbine air vents, the quite beautiful material and trim finishes and just the general solid feel are further typical contemporary Mercedes cabin treatments, as are the excellent ventilation and ample storage options.

And while rear vision isn't great, that's what cameras are for. It's all pretty much on brand.

It is a shame, given how elevated the Mercedes-AMG engineering is underneath, that the GT’s interior look and ambience is so similar to those of a (albeit higher-spec) C-Class or GLE. It's simply not as special as some of the company’s previous sports cars.

More annoyingly, the ride is too firm and bumpy for a GT, and this has the unhappy effect of provoking random rattly trim sounds within the cabin. It’s a bit like scrunched-up cellophane. In a $420K (as tested) Merc, that’s very disappointing, especially as it can be heard over the copious amount of road and tyre noise droning through, particularly on coarser bitumen surfaces.

Further back, the rear seat is strictly two-plus-two, and nobody over 150cm tall is recommended to travel there by Mercedes itself. That sloping roofline is the culprit. That said, brief trips with a bowed head are possible, as the fixed cushions and split-folding backrests are actually surprisingly comfy. But only for short journeys. Kids should love it though, and the second row does open up the GT’s usefulness enormously.

As does a near-doubling of the AMG’s cargo capacity, jumping 146 litres to 321L with backrests erect, to a whopping 675L (+325L) in two-seater mode. The flat floor is accessed via a large electrically-operated liftback door, offering quite a large aperture for easy loading/unloading.

Having no spare wheel helps here, with a tyre inflation kit included in lieu of that.

Meanwhile, at the front, under the bonnet, things have definitely changed for the better as well.

“Practicality” is about as relevant to this car as a code of ethics is to a drug dealer or a contract killer, because the SL63 buyer is hardly worried about cupholders and boot space. For what it's worth, there are four cupholders in the two-seater cabin (which might explain why owners aren't worried about their liquid carrying prospects) and a minimum boot space of 364 litres and a maximum - with roof up - of 504, which is actually not bad.

Cleverly, there's a little robot-operated luggage cover inside the deep boot that stops your gear from being crushed when the roof goes down.

There's also space in the long doors where you might secrete a bottle of wine that would get a NSW Premier fired if he thanks you for it, and a bin in the console to hide your phone.

It’s difficult to ponder the idea of value when a car is already approaching $400,000 at a rapid rate even before you start piling on the options. On the plus side, for a list price of $368,715 you do get an extremely long list of standard equipment.

The SL has always been completely unapologetic about its size.

Edited highlights include leather on almost every available surface, heated and cooled electric seats with a fan heater for your neck, a B&O stereo that will shatter the windscreen on request, aluminium trim that's real aluminium (mostly), Active Ride suspension, sat nav, dual-zone climate control, active cruise, LED headlights and a huge swag of safety gear.

The 12-speaker stereo also has DVD, limited smartphone integration via Mercedes' COMAND system, a seven-inch screen and, of course, Bluetooth.

There’s a plaque signifying which engineer “handcrafted” the GT’s engine – in this case, the famous M177 in 3982cc, 4.0-litre twin-turbo intercooled V8 petrol guise.

Delivering 430kW of power at 6500rpm and 800Nm of torque from 2500-4500rpm, it sends drive to all four wheels via a nine-speed multi-clutch transmission (dubbed MCT in AMG-speak), catapulting the GT63 4Matic+ from 0-100km/h in just 3.2 seconds, on the way to a top speed of 315km/h.

How does it do that?

With AWD, the GT is now nearly 15 per cent heavier than before, but it still manages a punchy 218kW/tonne. Active aerodynamics over, inside and under a more-rigid body structure also helps.

The AMG 4Matic+ AWD system goes from 50/50 front/rear, to 100 per cent rear, variable torque distribution according to conditions and settings, and backed up by an electronic limited-slip differential. Among the many driving settings are Race Start, Drift Mode and good-old Comfort, if it all becomes too much.

Also keeping all that performance in check is a high-performance composite brake setup with improved cooling for faster responses.

Interlinked active roll bars improve body control, the five-link independent suspension features adaptive dampers for a softer ride.

And, as for that 4WS tech, the rear wheels steer opposite to the fronts at up to 100km/h (by some 2.5 degrees) for tighter and tidier handling, or 0.7 degrees in the same direction above 100, for greater stability and road-holding.

Its effect on the way this near-two-tonne coupe zigs and zags around corners is something you need to experience to really appreciate.

The SL63 is powered by Mercedes’ increasingly famous V8, with two turbos along for the ride to add oomph and cut the car's famous consumption, at least slightly. The 5.5-litre unit produces a massive 430kW and a scarcely believable 900Nm of torque.

All of that heads rearward via a seven-speed dual-clutch transmission that helps sling the 4.6m, 1848kg machine to 100km/h in 4.1 seconds.

Actually, the GT’s economy isn’t horrendous considering how fast it can go.

Even blasting a few times around beckoning country roads, we managed an indicated 13.0L/100km, which is an improvement on what Mercedes-AMG says the GT averages the 14.6L/100km average that Mercedes-AMG officially states.

That translates to a carbon dioxide emissions rating of 334g/km.

Using 98 RON premium unleaded petrol, an average of just under 480km between refills of the 70L tank is possible. The urban run sees consumption rocket to 21.8L/100km (for just 321km of range), or 10.4 out on the highway run, meaning that over 670km is possible should you decide to drive in a docile manner.

Much as is the case with the price, there's no real way to soften the blow here - the SL63 drinks like a footballer on Mad Monday, except it does it every day. The official combined cycle figure of 10.2L/100km is quite easy to double, as we did, averaging 21L/100km in mostly flowing suburban traffic. In the car’s defence, the accelerator pedal spent a good deal of time near the firewall.

The SL does have stop-start to help reduce its considerable environmental impact.

Nobody will drive the GT63 4Matic+ and think, ‘Oh, this is OK’, because its breadth of performance is phenomenal.

No matter which mode you're in, from Comfort through to track-tuned Race, the Mercedes-AMG blends forceful pace and commanding control without ever breaking a sweat.

Flex your right foot and the two-tonne coupe bounds into action like a giant on a mission, striding past posted speed limit signs in nanoseconds and way, way faster than the law will stand if diligence isn’t exercised.

And there’s no point relying on seat-of-your-pants sensations, either, because the chassis below embraces the road with an almost zealous devotion. Which is astounding, given how agile the four-wheel steering-enhanced handling is.

The 63’s super power is exactly that – it dulls your sense of speed. One tester admitted to exceeding 150km/h before noticing. An odd confession considering the sonic boombox that is the bi-turbo V8’s howl.

But jailbait performance is not even the 63’s most lingering joy. That would be its steering perfection, that delivers that rare trifecta of keenness, crispness and communication. The wheel feels eager and alive in your hands, even when powering between tight turns, backed up by sensational grip and control. How can a two-tonne GT handle so sharply?

Warm, dry roads were the order of the day, so we can’t tell you how the 4Matic+ permanent AWD system deals with wet or slippery surfaces, but the slick multi-clutch transmission, seamless torque-vectoring tech and sticky tyres more than cope with the 63’s formidable outputs.

So, that's the gushing part out the way, then.

Despite the adaptive dampers, rigid architecture and exquisitely sophisticated suspension, the ride is simply too stiff in Comfort mode, and downright jittery on some of the Tasmanian roads we tested on, for the 63 to be considered a true luxury grand tourer. It just isn't comfortable, luxurious or supple enough.

Plus, grippy as they are, the 21-inch wheels transmit too much road and tyre noise through to the cabin, meaning that the GT isn't as quiet as you'd hope. Add the aforementioned trim squeaks, and the expected cocooned silence isn’t always there.

The upshot is that the 63 possesses more of a sports car character than a luxury GT character. Great news if you're a 911 type buyer and are seeking a high-performance 2+2 alternative, but a disappointment if comfort and refinement are priorities.

Still, it is impossible not to be deeply moved by this Mercedes-AMG.

There are a number of impressive things about the way the SL drives. Firstly, astronauts will be familiar with the galactic thrust of the V8. It seems endless, seamless and ready to sling the big coupe into the outer atmosphere. Few engines of any kind can match the relentless go on offer in the SL and much of the credit should go to the seven-speed twin-clutch transmission.

When you jump on the brakes and shift down, the exhaust keeps the show going with angry crackles and pops.

Containing a torque figure like the twin-turbo V8's requires a lot of electro-trickery to stop you from being launched off the road. The great thing about all that stuff is that it works unobtrusively and smoothly.

Mashing the carpet in an SL without traction control would create much sound and smoke but little forward progress, such is the twist on tap. The SL has a range of modes from full-nanny (which is meant to keep you on the slippery Alpine road you've chosen to get you to some Swiss ski resort) while turning the dial all the way around to Race loosens the bonds.

It's in this mode you'll have the most fun and it does seem that the intermediate settings are a bit of a waste of time. Race mode does little to diminish the amazing ride quality provided by the active suspension setup, but relaxes the reins on the huge rear tyres. Exiting roundabouts is suddenly a huge laugh, with the tail cheerfully breaking traction and the two-mode exhaust thundering in a most pleasant way.

Better still is that when you jump on the brakes and shift down, the exhaust keeps the show going with angry crackles and pops, with more on the way when you lift off. There's little to match the aural pleasures of a properly tuned V8 and Mercedes has resisted the temptation to quieten it down on the outside and generate a fake noise for the inside. Although that would be stupid in a convertible, if you think about it.

The SL63, despite its AMG badge, isn't about all-out handling, of course. The Ferrari California would definitely show it how it’s done on a winding country road. The SL is more about flow, building momentum and rarely shifting down to second gear. The monstrous torque is enough to keep things rolling but should you wish for a bit more of the exhaust bellow, second is there for the taking.

Hustling the big convertible feels wrong, not because it can't do it, but because it's not really what it's for. Having said that, it offers a kind of fun that nothing else on Earth will provide, not even a Bentley GTC.

With the roof up, the SL63 is a quiet place but not remarkably so. The huge sticky tyres do the cabin's hush no favours, with an annoying roar on a wider range of surfaces than you might expect.

Roof down, it's hardly a paragon of virtue. A lot of wind noise reaches the cabin, even well below the huge speeds the SL can reach. So if you want to talk, it's windows up you'll need to deploy the mesh screen that bridges the roll hoops.

Six airbags, ABS, stability and traction controls, blind-spot sensor, lane-departure warning, brake assist, active safety bonnet, lane-keep assist, driver attention detection, AEB.

What’s the GT like to own?

Mercedes-Benz offers a five-year/unlimited km warranty, with five years of roadside assistance. This is average for most mainstream and luxury brands, but superior to most sports-car makers like Porsche and Lamborghini.

Intervals are every 12 months or 20,000km, and while no capped-priced servicing is offered on the GT, pre-paid three-, four- or five-year service plans are available, ranging from $5165, $7700 and $8665 respectively.

Big performance demands big maintenance bills, it seems.

The SL63 is covered by Mercedes' three-year/unlimited kilometre warranty. And, er, that's it.