Gazing up at the mountain access track, I was torn. A big, blue sky, swept with curls of high cirrus, stretched out above the valley and the view from the top promised to be something special. I knew the BMW X5 beside me would be mechanically capable of the climb - rain-channels, gravel and fist-sized pebbles would be easily dealt with by the intelligent xDrive system in the big SUV - but not on these wheels.The seven-spoke 20" alloys, shod with puddle-splitting, low-profile Michelin Radial Xs, looked gorgeous but were no way up to this job. Putting a quarter of the car's 2.18-tonne weight onto one of those, then balancing it on a pointy stone, looked like a mistake so expensive you'd only make it once. I shook my head sadly and pulled back onto the metalled surface.On the road, though, those sad shakes of the head were few and far between. This test car had the three-litre straight-six turbo diesel engine under its elegantly sculpted and strategically vented bonnet. It mills out 218bhp and 369lb/ft of torque. When fed through the six-speed semi-automatic gearbox, that means there's no excuse for being last away from the lights.BMW says the car will hit 62mph just 8.8 seconds from the word go, but in fully automatic mode I found there's a short delay between stamping down and the car leaping forwards. If the figures are correct, I'd suggest the car spends the first second thinking about the best way to do it and the next 7.8 seconds catching up.Once you're used to this momentary hesitation, the car's road manners are impeccable. The gearchanges are so smooth as to be almost seamless. If you want you can use the stick to click sequentially up (pull back) or down (push forward) through the cogs but the changes feel relatively sluggish. Besides, since the fully automatic system will change down and hold a low gear if you brake on a downhill, the semi-auto mode is rarely much advantage on the tarmac.The suspension on this Sport model is half an inch lower than standard and features air springs all round to keep the car level through corners, while accelerating, under heavy braking and no matter what you have in the boot. It works too. After around 800 miles of everything from motorway to mountain pass, laden with three other people and their luggage, I can say it felt more stable than should be possible through the bends, and firm but not uncomfortable on the straight.In fact, the whole tenor of the X5 is firm but not uncomfortable. The steering and the pedals feel a little stiff at first, but that all works to its advantage. The seats all round are relatively solid but well shaped and supportive - particularly the electrically adjustable front seats. Even the way the doors and the tailgate open and shut add to that impression of rock solid integrity.Indoors, the accommodation is capacious enough for five adults and the boot is a big, square load-swallower with easy slide-it-in access over the split tailgate. The car's well laden with equipment too. A multi-media screen in the main console is the nerve-centre of everything except the his-'n'-her climate control that sits separately below it.Through a series of conventional knobs and buttons you can navigate with surprising ease through the sound kit, the Bluetooth phone set up, the satellite navigation equipment, the onboard systems and trip computer, and even the multi-channel telly you can use when you're stationary.Visibility all round is as good as you'd expect in such a high, square vehicle, and the nearside mirror turns down to help you reverse in close to the kerb. You don't always want that mirror thing, particularly when backing through gaps, but the audible proximity alarms should prevent you accidentally crunching your 40k worth of metalware into a bollard.So why would you buy it? Well the essence of the X5 3.0d Sport is a combination of surreptitious performance and ostentatious class. In other words it goes like the clappers even if it looks like it shouldn't, while at the same time it's currently the biggest way of announcing that you run a BMW.If you're on the inside it's roomy and comfortable with an environment that's hushed, even when that diesel engine is cold. From the outside it's unmistakably a BMW from any angle so it carries all the kudos of the blue and white badge. It'll also keep its value better than most, with specialists suggesting it will be worth 70% of the purchase price after three years and 36,000 miles.The downsides are limited but important. It is expensive and will only seat five people where many other luxury 4x4s in this price range are offering a versatile seven-seat option. The driving environment, while classy, does feel a bit dated and some of the metallic plastic trim lets it down. The other thing is that there are a lot of X5s on the road, so if exclusivity is your bag you'll be disappointed.Space and/or image have to be the selling points on the X5 3.0d Sport since the mud-plugger kit will be superfluous most of the time. The intelligent 4x4 system, which puts power to the axle with the most traction, will be of some use in the winter slipperies or if you're towing, but I can't imagine when you'd ever need the hill descent control. The lack of the variable ride height that's available on other models, and the big performance tyres I've already talked about, emphasise that the Sport is primarily a road car.If anyone points to the mud and rubble and tries to convince you otherwise, just quote singer/songwriter Kirsty MacColl when she sang: "In these shoes? I don't think so." Engine 2993 cc, 6 cylinders Power 218 bhp @4000 rpm Torque 369ib/ft @2000 rpm Transmission 6 speed semi-auto Fuel/CO2 30.1mpg / 250 g/km Acceleration 0-62mph: 8.8sec Top speed 130 mph Price From £39791.00 approx Release date 15/01/2004