BMW 320d vs BMW 6 Series

What's the difference?

Over 44 years BMW has produced more than 15 million examples of the 3 Series. That's roughly one every minute and a half... for over four decades.

And the latest, seventh-generation version of what the famous German maker defines as the "heart and soul" of its brand has landed in Australia.

The new '3' is longer and wider. It's also claimed to be slicker aerodynamically, up to 55 kilos lighter, more fuel efficient, and faster.

And it'll need every advantage it can muster to take a chunk out of its arch rival, the all-conquering Mercedes-Benz C-Class.

What happens when you struggle to sell an odd-bod, not-quite-a-coupe, sort-of-a-hatchback, almost-an-SUV model? Well, sometimes it gets axed, and replaced with a new model that bears a new name.

That's pretty much it in a nutshell for the BMW 6 Series Gran Turismo, which was formerly the 5 Series GT. It essentially takes the place of the 6 Series Gran Coupe - an alternative to the regular 5 Series sedan that's more attainable than a 7 Series limousine.

Confused? It's not as difficult as all that sounds - you just need to know that this model, the 2018 BMW 6 Series Gran Turismo, is supposed to offer a neat alternative to the go-to family luxury car or SUV.

I spent some time in the entry-level 630i to see if it can deliver on that promise. In fact, I spent more than 24 hours driving the BMW 6 Series GT over the past week, and I don't have a sore back, I haven't been left scratching my head over the intended purpose, I haven't been uncomfortable, and I haven't been left wanting for much.