Compare the Porsche 911 Carrera GTS Cabriolet PDK - [2017] vs Mercedes C Class 63 S Saloon - [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 Porsche 911 Carrera GTS Cabriolet PDK or the Mercedes C Class 63 S Saloon. We'll leave it up to you to decide which is your favourite.