What's fastest? 911, SLS, LFA or GT-R?

Which of the various mega-horsepower supercars is the fastest of all? We pit the Mercedes SLS against the Lexus LFA and the Nissan GT-R against the Porsche 911 Turbo S to see which car can claim that title. But to claim the crown, the winners of the two head-to-heads will also have to beat a special challenger from Britain... Jamie Corstorphine is your referee.