OK, so the 400bhp V8 from the M5 would have been nice, but the X5's automatic gearbox can't handle its extra torque, so you'll have to get by with a 4.6-litre version of BMW's regular V8. Still, with 347bhp and 354lb ft, the X5 4.6is has plenty of firepower to back up the promise of its bulging flanks, jutting exhausts and giant hunks of rubber. Until Porsche releases the Cayenne, this is where it's at in the world of the Sports-Brute.

The original 4.4-litre X5 isn't exactly a slouch with a 0-62 of 7.5sec and a 143mph maximum, but the 4.6's extra 60bhp and 30lb ft of torque slice a full second off the 0-62mph time - 6.5sec makes it Boxster-quick, which is quite a thought - while a top speed of near as dammit 150mph is plenty to be going on with.

I'll be honest. I wanted to dislike the X5. As far as I'm concerned, driving this car is the equivalent of walking around with a Rottweiler straining at the end of a lead. True, a Range Rover is even bigger (the St Bernard of 4wds, if you like), but the X5 4.6is adds an extra helping of aggression. Fine if you view driving as some sort of warfare - if they get hit by this they stay hit, that sort of thing - but I'm not certain it's what the world needs right now. And isn't there just the faintest hint of vulgarity, a momentary glimpse of Chigwell in the glint of the alloys and the optional aluminium running boards?

Pity you can't separate the driving experience from the image this car projects, because the second you turn the key you just know the X5 4.6 is absolutely steeped in the stuff that turns us on, the stuff we call evoness. The bored and stroked V8 emits a throaty burble that sounds like X5 has been hanging out with a gang of TVRs, and the way it leaps off the line is very pleasing indeed. Acceleration is formidable all the way from 3500 to 6000 revs, though there's little to be gained taking it to the 7000 red line.

The whole feel of the chassis is transformed by the monster footwear ί¿½ 9.5 x 20in wheels wearing 275/40 Michelin Diamaris at the front, 10.5 x 20-inchers and 315/35s at the rear. What was a bit of a pussycat now feels almost tigerish. The downside is that the ride gets a bit fidgety on urban brokentop - you can feel the big tyres shouldering compressions - though it smoothes out when you start reeling in a ribbon of B-road.

It's the connectedness that impresses. You tap into what's going on at the road surface through the meaty steering and the seat of your pants. Booting it out of a T-junction, you're aware of a transitory slip at the back, then the torque is channelled forward and you can feel the front tyres clawing at the tarmac before all four wheels get hooked up and convert all that energy into forward thrust.

Powering hard out of a 60mph corner, you feel the back end compress, the inside front go slightly light as it starts to lift. On any half decent surface the X5's composure and cornering grip are remarkable, while the brakes, now featuring slightly larger front discs, seem well up to fast road driving. The five-speed auto is as slick as ever; slide the gearstick across into Steptronic mode, the choice for cross-country running, and you really can cover the ground.

The further you drive, the faster you go, the more impressive the X5 becomes. It actually does feel like a sports car on stilts - and sounds like one too. It shrinks around you until you almost forget what you're driving. Which, in my book at least, has to be an advantage, though doubtless plenty of others will give it a last lingering look back when they clamber out.

Fantastic though it is, the price is a pretty steep-looking ΂£54,000. That's almost ten grand more than the 4.4i Sport (the test car came with a further ΂£4675 worth of options, including the sat-nav/phone/TV Communications Pack at ΂£3395). The X5 4.6is makes a pretty good fist of being a sports car. But to look at it another way, for the price of a top-spec 4.6is you could have an X5 3.0i Sport and a Lotus Elise. It won't be quite the same ego trip, and you won't intimidate as many of your fellow road users, but you might just have even more fun.