Rare are the occasions in life on which just one solution fits all, even when it comes to BMWs that have four doors and five seats and which can fire you at the horizon with broadly the same conviction as a bullet that has just appeared out of a gun.
Because for every fast factory BMW, there is inevitably an alternative available from Alpina. And in this case the alternative is genuinely quite some weapon.
So we posed one very simple question to which the answer is anything but straightforward. In a fast BMW 3-series – a very fast BMW 3-series – which is the best form of engine to have thumping away beneath the bonnet: petrol or diesel?
At one time the answer would have been an entirely predictable ‘petrol’, thank you very much, move on, nothing else of interest to be seen here. Nowadays, though, with the advent of the monster that is the Alpina D3 Biturbo, the answer is nowhere near as simple as that. Not even when the petrol-powered 3-series comes in the form of the mostly brilliant new BMW M3.
The similarities between these two ultimate 3-series are, of course, many, which is hardly surprising given that they share the same fundamental bodyshell, the same rear-wheel drive chassis, the same suspension layout and the exact same cabin and boot dimensions.
But beyond these elements they go about achieving what they do in very different ways from one another, and in the end those disparities are, in places, quite shockingly apparent.
The M3 is propelled by a twin-turbocharged 3.0-litre straight six petrol engine that produces a full 425bhp along with a decent slug of torque – 406lb ft, no less, between 1800 and 5500rpm. It also has the ability to rev to 7500rpm and beyond.
The D3’s twin-turbo six-pot diesel engine, on the other hand, is all done by 5000rpm, and although it summons rather less power than the M3 (345bhp), it has massively more torque up its sleeve. The amount it produces is almost hilarious, in fact, with an eye-watering 516lb ft being available from just 1500rpm.
So despite the fact that the 1660kg D3 weighs a touch more than the 1635kg as-tested M3, in theory it can all but level with the factory car in a straight line.
Its standard automatic gearbox also has one more ratio to play with than our M3 test car’s optional seven-speed dual-clutch automatic unit, but crucially, the Alpina costs a not insignificant £9225 less than the M3.
Perhaps an even bigger difference between them is the way their respective chassis, steering and suspension systems have been tuned to behave once on the move. Both can be adjusted electronically through a variety of programs to become sportier or more comfortable, depending on the kind of road you’re driving on. But in all of its various modes, the M3 always feels the sportier of the two.
It has a thicker, slightly bigger steering wheel than the D3, and there are three different weights that can be dialled up to suit the desires of whoever happens to be grasping it. But no matter which setting you put it in, the M3 always feels more urgent, more uptight, keener to let rip and, perhaps, also a touch more neurotic beside the more relaxed and slightly less manic D3.
And right there is the key difference between these two super-swift 3-series. Their characters, despite appearing to look quite similar to one another outwardly, couldn’t be more opposed on the inside.
At its heart, the M3 feels like a wild dog that’s straining continuously against its leash; the D3 is the cuddly old hound that has seen it all, done it all and doesn’t appear to be interested in doing much beyond what you ask it to.