Oh dear - this is a dilemma. On the one hand, it's great news that BMW is now selling its triple-turbo diesel in the UK. On the other, the first time we're driving it on home turf is in the X6, thereby marrying one of our favourite bits of BMW (this engine) with one of our... less favourite (the X6). Joy mitigated by a sense of slight footballer-chic pointlessness.
Still, let's concentrate on positives. The triple-turbo 3.0-litre diesel - also available in the X5 - is a monster. Thanks to 376bhp and 546lb ft, it'll manage 0-62mph in 5.3secs, in a car weighing 2.2 tonnes. To put that into perspective, the Audi Q7 V12 (lord of insane diesel power) hits 62mph in a languid 5.5.
But this is about more than figures. It's about what the X6 M50d lacks. And what the multi-blower engine lacks is lag. Thanks to the arrangement of the turbos (two small ones for lower revs and a larger one for higher up), there isn't any lag in the rev range. It's brilliant. And then there's the flipside. Drop the eight-speed auto into flappy-paddle mode, and experience an entirely different X6. It's now all about scary speed and a never-ending torque curve. The instant pace is addictive - anyone worrying that turbo engines might spell the end of gratifyingly reactive power shouldn't be concerned any more. And unlike other diesels, the M50d doesn't run out of puff at the top of the rev range. There's torque and power available all the way to the red line.
It helps that there's nothing flaccid about the X6. Body control is superb, the steering precise, the torque-vectoring a marvel. OK, it's not fun in the traditional sense, simply because there's so much grip available for the feedback on offer, but it is massively fast.
To be honest, the X6 is happier being driven hard. The ride is too firm and the engine note too gruff to suit pootling. Blame BMW's new M Performance trim with its big wheels and sports suspension, the sole spec on the M50d. This is meant to be a halfway house between a full-on M car and the lighter touch applied to M Sport models, but in the X6 it aggregates into too much. In a very un-TG verdict, the X6 M50d might be better if it were eased back and made more relaxed. Better still, if this engine were in the 5-Series Touring. There wouldn't be any dilemmas then.
2993cc, 6cyl, 4WD, 376bhp, 546lb ft, 36.7mpg, 204g/km CO2, 0-62mph in 5.3secs, 155mph, 2225kg
As an engineering achievement, it would be an easy 9/10. But it's still an X6, so we have to knock a point off...