A lot of it has to do with the type of clutch you are using as has already been stated. You can have two main types in 7.25 inch AP type - these being sintered which is basically metal on metal and only meant for circuit use as they have no slip at all, or ceramettalic which is used mainly for hillclimbs and rally cars where a degree of slip is available. A good hydraulic clutch set up also helps a hell of a lot if using a ceramettalic on the road