Compare the Bentley Continental GT Speed 6.0 W12 Bi Turbo Convertible - [2016] vs Porsche Cayenne Turbo S 4.8 V8 - [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 Bentley Continental GT Speed 6.0 W12 Bi Turbo Convertible or the Porsche Cayenne Turbo S 4.8 V8. We'll leave it up to you to decide which is your favourite.