If you're on a budget, try Toyo R888s or Nitto NT-01s. These tires do not have to be shaved and they are designed with endurance racing in mind.

I run the Nittos in sprints and I've gotten 6 weekends out of a set driving a pretty heavy car. Also, some magazine reviews do not seem to suggest that the Hoosier R6 is terribly faster than the Nitto. (And who drives flat out for 12 hours so as to derive the max. benefit from stickier tires???)

My $0.02? Try the Nittos. They are cheaper than the Toyos, offer similar performance, and I doubt you'd be disappointed.