Compare the Radical RXC 3.7 V6 - [2014] vs Mercedes SLR Class McLaren 722 S Roadster - [2008]. 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 Radical RXC 3.7 V6 or the Mercedes SLR Class McLaren 722 S Roadster. We'll leave it up to you to decide which is your favourite.