In this episode of Fifth Gear Tiff Needell and Karun Chandhok take two high performance saloons to the track to discover which is the fastest, and most entertaining, to drive. BMW have a long history of producing very quick family sized cars, and on paper their new M4 looks every bit as good. By comparison Lexus has never made a car of this type - however their new RC-F seems to match the BMW blow for blow. Three tests will determine which car best deserves its £60,000 price tag. The Bentley Mulsanne Speed is, according to the manufacturers, the fastest limousine in the world. But, being a Bentley, it's extremely luxurious to. Jonny Smith takes a tour of this £300,000 car, which has a top speed of 190 mph but also comes equipped with Champagne flutes.