If you are a single driver, then what Dave said is true; you'll have a hard time generating the heat necessary to make the tires truly effective.
I can think of a few select times when using R6's might work: If you are campaigning a dual-driver car on a day where the ambient and ground temperatures are high, the R6's may be more effective. Basically it comes down to heat management, as once the tires get overheated, they certainly will make driving more difficult.
Mark Valera
2001 Chevrolet Camaro Z/28 "1NE"
FS #93