Compare the Ford Sierra Sapphire RS Cosworth 4x4 - [1990] vs Ford Mustang GT Convertible 289 4.7 V8 - [1966]. 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 Sierra Sapphire RS Cosworth 4x4 or the Ford Mustang GT Convertible 289 4.7 V8. We'll leave it up to you to decide which is your favourite.