| First Drive | Munich, Germany | BMW M550d xDrive |
Key Facts
Engine: 3.0-litre triple turbodiesel
Transmission: Eight-speed automatic, four-wheel drive
Body style: Four-door saloon
Rivals: Audi A6 BiTDI quattro, Mercedes-Benz E 350 CDI, Lexus GS 450h
CO2 emissions: 165g/km
Combined economy: 44.8mpg
Top speed: 155mph (limited)
0-62mph: 4.7 seconds
Power: 381hp at 4,000- to 4,400rpm
Torque: 740Nm at 2,000- to 3,000rpm
In the Metal: 
If an M car can be quiet then this is it. The external changes are minimal, with deeper air vents up front, a small lip spoiler at the rear and some trapezoidal tailpipes. That stealth is even more apparent on the pictures here, as instead of the standard 19-inch light M alloy wheels it's on more conventional rims and winter tyres. As a sleeper Q car the M550d xDrive is about as good as it gets.
Inside there's the usual smattering of M badging, a leather/Alcantara steering wheel, aluminium hexagonal trim inserts and M Sports seats. Subtle, but very effective, the 5's cockpit is one of the best around - even in lesser models.
Driving it:
Forget any diesel preconceptions as the three-turbo 3.0-litre six-cylinder unit not only goes very well but sounds fantastic, too. BMW won't say exactly how it has achieved it, but some clever sound management ensures that the M550d's unit sounds like a petrol V8 engine. Quiet at idle and around town, it all feels a bit ordinary until you really push it. Do so and the engine's urge is incredible, the triple turbo set-up removing it of any diesel-like lethargy. This is a diesel that thrives on revs with sustained progress where rivals tail off. Add an eight-speed automatic transmission that's swift and slick in its operation and the 550d xDrive offers scarcely believable but utterly effortless pace - if anything the gearbox could do without kicking down sometimes and letting the engine do the work.
There's nowhere that it feels slow, the linear shove present from low revs, while the high-rev responsiveness and quite extraordinary ability to gain pave from already high speeds with so little apparent effort is staggering. That's backed up by a chassis that's been given an M makeover. Not quite as focused in its set up as full-one M cars, the ride errs a bit more towards comfort while retaining excellent control, though the steering is a bit light on information and consistent weighting.
It's not obviously four-wheel drive, the bias remaining rearward with effort only really sent forward when it's required. No doubt fairly regularly with 740Nm to manage, but it is all done without ever being obvious at the wheel. What is evident is the car's dual nature. It can be driven in Eco Pro mode for ultimate economy (officially it returns 44.8mpg on the combined cycle) or as a ridiculously rapid cross-country machine in Sport or Sport+ modes.
What you get for your Money:
It's pretty well loaded as you'd expect for a car that's the oily sister of the BMW M5. You can still go daft on the options list with things like night vision, but there's no need to. Sadly, the M550d xDrive is only available in left-hand drive - though there's nothing stopping you from importing one and sitting on the 'wrong' side of the car.
Worth Noting
The M550d xDrive might never make it to the UK officially, but the engine will. It'll feature in X5 and X6 M50d cars - mixing economy with thumping performance and presence. The M550d xDrive might make it to the UK in a future generation, but M insiders say it won't come over in its current guise. There is a - very - slim chance that it could be offered in rear-wheel drive only, but don't hold your breath.
Summary
M division's people admitted that the M550d xDrive has been built specifically with a typical customer in mind - wealthy skiers. Until now, they have needed to go to Audi for fast, four-wheel drive transport with decent range. Audi should be worried. Very.
