Compare the Porsche Cayman GT4 3.8 981 - [2015] vs Bentley Continental GT Speed 6.0 W12 Bi Turbo - [2016]. 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 Porsche Cayman GT4 3.8 981 or the Bentley Continental GT Speed 6.0 W12 Bi Turbo. We'll leave it up to you to decide which is your favourite.