Compare the Porsche 911 Carrera 4 991 - [2012] vs Mercedes SL Class 55 AMG V8 R230 - [2001]. 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 911 Carrera 4 991 or the Mercedes SL Class 55 AMG V8 R230. We'll leave it up to you to decide which is your favourite.