All the following are available in the typical 17" sizes of 275\40-17 and 235\45-17 and are in the same performance category to the KU36 (extreme performance as per tirerack
http://www.tirerack.com/tires/types/....jsp?perf=EP):
Nitto NT05, UTGQ = 200 (although some sizes have a UTQG of 140)
Falken RT615\k UTGQ = 200
Toyo Proxies R1R, UTGQ = 200
KU36, UTGQ = 180
Lots of other options with a similar rating up to size 255\40-17, but these are the only ones Ive found that go up to 275.
I know we probably don't want to make it too complicated but possibly going off the UTGQ rating should be considered. Just say tyre must have a UTGQ of 180 or greater? That would really open up the class to nearly anyone less than R-Spec