The 3.5sd Twin Turbo diesel engine is one of BMW's best yet and, as others have already said, has been available in Europe for well over a year now and in various other models, as well as the X5.
It also responds fantastically well to a remap - here in the UK we can achieve a bhp increase from the stock 286 to 326, and a storming torque increase from 580nm to 650nm with (assuming no lead boots on the driver
) a small improvement in fuel consumption as well! Any remnants of turbo lag (and there isn't much to start with on the twin turbo) are smoothed out.
Just as a guide,the e60 M5 only has 520nm of torque as standard from the factory!!