Compare the Audi A6 S6 3.0 V6 Turbo - [2017] vs BMW X6 M 4.4 V8 Turbo E71 - [2013]. 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 Audi A6 S6 3.0 V6 Turbo or the BMW X6 M 4.4 V8 Turbo E71. We'll leave it up to you to decide which is your favourite.