So if you want a huge and hugely powerful BMW you need to look to Alpina, the tiny and masterful BMW tuner, and specifically to its new 500bhp supercharged B7.

It's that last detail that's important. BMW will turbocharge diesels or accept the need for a supercharger on the Chrysler-designed Mini Cooper S engine, but you won't find forced induction on a BMW petrol-engined car. Not now, not in the future. The beauty of this policy is that we get to look forward to a 5-litre V10 capable of revving to well over 8000rpm in the next M5. The downside (if you're eager to keep up with the Mercedes-owning Joneses) is that BMWs will never be able to match the huge torque figures that define those super-Mercs. Alpina, on the other hand, is happy to use forced induction if it allows for a more relaxing and more refined delivery, both qualities for which Alpina is famed.

The B7's engine is based on the silky 4.4-litre V8 found in the 745i, amongst others, and features a nautilus-type radial supercharger to create its enormous 500bhp at 5500rpm and 516lb ft of torque at 4250rpm. As you'd expect of a blue-blooded Alpina engine, it remains impeccably mannered with no hint of supercharger whine either when crawling through traffic or under full load. It's a mighty unit, too, pulling hard from 2000rpm and gaining in ferocity with every extra rev.

Between 4000rpm and the rev limit at 6200rpm, it's phenomenal. Not 600bhp-blunted-by-a-hefty-kerbweight-phenomenal but oh-my-God-my-face-hurts-phenomenal. If the Mercedes S55 AMG is any quicker it's only in the low- to mid-range and it loses out in both crispness and sheer energy at the top end. Alpina claims the B7 will sprint to 60mph in 4.8sec and run on to an unfettered 186mph. And the good news is that Alpina's lastest masterpiece will find its way under the bonnet of both the 5- and 6-series in the near future.

The forthcoming B5 and B6 models will undoubtedly be crushingly quick, but the B7 doesn't give too many clues about how they'll compare dynamically with the hardcore M products. It's an enormous car, dwarfing our Audi S4 camera car and towering over the RS6 Plus that I arrived in (more of which, later), and as such it's not really a cut-and-thrust driver's tool. It handles neatly enough and has strong grip and decent traction (thank the 285/30 ZR21 Michelin rubber for that!) but it's still a 1950kg 7-series. That's a useful 140kg lighter than the 760i, and because the V8 is substantially shorter than the V12, the weight is lost in the right place.

Once you've felt the dizzying power, it's tempting to go M3-chasing. You'll certainly haul them in and spit them out on the straights, but you'll find understeer will slow you through the corners if you're trying to maintain the advantage. Turn the traction control off via the iDrive control system and the B7 remains faithful, spinning its wheels but rarely sliding into oversteer. It certainly feels more on top of its power than the equivalent Mercedes S-class,
occasional understeer or not. And the superb Switchtronic six-speed automatic is adept at deploying the V8's thumping power.

You can switch between the normal shift pattern, a Sport mode and full manual control (operated by two buttons, one behind each horizontal spoke of the steering-wheel) via a switch on the wheel. Sport is probably a bit too aggressive but the manual mode works brilliantly. You can even heel-and-toe to match engine revs if you're on a charge.

Alpina has done a fine job turning the 7-series into a deeply fast and effective supersaloon. Whether you want one depends on whether you like the donor car's styling. I do and I do. It's every bit as fast as an S55 AMG, feels more special and at ΂£76,500 fully loaded, it's ΂£11,000 cheaper, too. As I mentioned earlier, I arrived at Sytner of Nottingham to collect the B7 in the new 473bhp RS6 Plus. It had felt awesome in the morning, a real step on from the standard RS6, but on the way home I couldn't help craving a bit more top end. Enough said.