Good street tires vs. used Rcomps

[hooRAH]

I have a bit of an academic question, as the result doesn't really matter, I'm just interested in the answer before I find out for myself.

A shop that I go to from time to time competes locally in an E36, I have an E46, and we are both running the same Kosei K1 wheels in 245/40/17. They've offered to let me finish off their used race tires (mostly Toyo R888s and other R-comps, not full race tires, at least they havent mentioned the full race tires) for pennies.

I am not familiar with Rcomps or race tires, but from what I've read, the only reason you'd throw away a performance tire with tread remaining is because its had too many heat cycles and doesn't grip well enough (and by enough, I mean enough to race competatively). So, my question is, when a track tire has too many heat cycles and doesn't perform well, are they still better than street tires? Or does the performance drop off that much that I'd be frustrated with them? Keep in mind I've only done a few track days and currently am still running street tires, but just bought a second set of rims so will now be running dedicated tires for the track.

Thanks guys.