Compare the Audi A5 S5 4.2 Quattro - [2007] vs Porsche 928 GTS 5.4L V8 - [1991]. 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 Audi A5 S5 4.2 Quattro or the Porsche 928 GTS 5.4L V8. We'll leave it up to you to decide which is your favourite.