Compare the BMW X7 M50d 3.0 Turbo - [2018] 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 X7 M50d 3.0 Turbo or the Mercedes SL Class 300SL Roadster W198. We'll leave it up to you to decide which is your favourite.