Don't even think about the 40i if that is what you're looking for. M50i will pop and crackle a bit more than 50i with m-sport, but the latter is still pretty good. But it's extra $$$. My advice, would be 50i with m-sport and put the extra $$$ towards a nice set of 22" rims with 315s in the rear. If money is not an issue, just wait for the x5 m.