Compare the Ford Focus 2.5 RS - [2009] vs Mercedes SLK Class 350 Auto - [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 Ford Focus 2.5 RS or the Mercedes SLK Class 350 Auto. We'll leave it up to you to decide which is your favourite.