Compare the Ford Sierra XR4i 2.8L V6 - [1984] vs Bentley Continental R 6.8 V8 Turbo - [1991]. 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 Ford Sierra XR4i 2.8L V6 or the Bentley Continental R 6.8 V8 Turbo. We'll leave it up to you to decide which is your favourite.