No personal experience with either but the R6 is THE tire of choise at Hallet. Literally half of the R compound tires out there are Hoosiers. Seems like the R6 would be the safe bet. Also, you might ask your dealer about it but I've heard that there are two different compounds available and with our heavy cars you really want the "endurance" compound. Like I said, this info is second hand, but it's from a guy running a GT500 in the GT1 class.