I've run Azenis RT-215, Azenis RT-615 and Hankook R-S2's on my track cars. They both seem to grip about the same under optimal conditions, but the Azenis definately can overheat and fall off very fast, taking a while to recover. I drive pretty hard and haven't really overheated the R-S2's. If I have it wasn't nearly as noticable as the Azenis.
The R-S2 does need to be scubbed in or shaved first. They pretty much suck at full tread, but once worn down to 3/4 tread left or so they are great, and get much better with wear, all the way down to the cords. The R-S2's are also better in the wet than the Azenis.
We are running 195/60R14 R-S2's on our E30. Good enough for 2nd fastest lap time at Stafford. I wish we could afford to buy 15" rims so we could get 225/40R15 tires. The wider tires would not only handle better, but last longer.
-Scott
Scott Barton