New Mercedes SL models don’t come along very often. There have been only six generations since the original 300SL. So can this lighter, faster, more efficient 430bhp twin-turbo V8 Mercedes SL500 live up to expectations? Read the review at http://www.autocar.co.uk/CarReviews/FirstDrives/Mercedes-Benz-SL-500-4.7-V8/261634/