Compare the Mercedes S Class 63 AMG Cabriolet - [2017] vs Porsche Cayman GT4 3.8 981 - [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 Mercedes S Class 63 AMG Cabriolet or the Porsche Cayman GT4 3.8 981. We'll leave it up to you to decide which is your favourite.