Compare the BMW i8 1.5 Turbo Hybrid - [2013] vs Mercedes SL Class 300SL Roadster W198 - [1957]. 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 BMW i8 1.5 Turbo Hybrid or the Mercedes SL Class 300SL Roadster W198. We'll leave it up to you to decide which is your favourite.