Compare the BMW 8 Series M8 Cabriolet 4.4 V8 Turbo F91 - [2019] vs Porsche Boxster Spyder 3.8 981 - [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 BMW 8 Series M8 Cabriolet 4.4 V8 Turbo F91 or the Porsche Boxster Spyder 3.8 981. We'll leave it up to you to decide which is your favourite.