Compare the BMW X5 4.8i V8 - [2008] vs Audi A8 3.0 TFSI Quattro - [2010]. 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 X5 4.8i V8 or the Audi A8 3.0 TFSI Quattro. We'll leave it up to you to decide which is your favourite.