Compare the BMW X6 M 4.4 V8 Turbo E71 - [2013] vs BMW 7 Series 750i xDrive 4.4 V8 Twin Turbo - [2015]. Find out which car is the fastest, most powerful, lightest or has the biggest engine in our top trumps style comparison page. Find out which car has the highest top speed or is the fastest accelerating, is it the BMW X6 M 4.4 V8 Turbo E71 or the BMW 7 Series 750i xDrive 4.4 V8 Twin Turbo. We'll leave it up to you to decide which is your favourite.