Put the R8 on slicks and repeat.
If you have tyres that can only get you around a corner at 66mph, then no matter how much horsepower you have, you will go around that corner at 66mph and no faster. If you stick slicks on and can go around at 76mph, you only need enough power to get that extra 10mph. Obviously the R8 will steam along the straights faster though.
It shows how much of a difference the tyres make really. I know the clio's on sorted suspension but the R8 ain't exactly on cart springs either.