I gotta agree:
BMW X5 M looks great in silver bmw-x5-m-silver-2 ? BMW BLOG ... that's one menacing machine in silver about to overtake you. The lines are great. The large front vents work because the vehicle is a bit lower.
But that rear is pretty weak:
http://www.bmwblog.com/2009/08/30/bm...x5-m-silver-3/ 
- needs wider stance or thicker rears
- exhaust area is customary M styling, but on a large vehicle like this it needs some work. It looks like a bolt-on there.