Compare the Bentley Continental GT Speed - [2012] vs Porsche 911 Carrera S Cabriolet 991 - [2011]. 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 or the Porsche 911 Carrera S Cabriolet 991. We'll leave it up to you to decide which is your favourite.