What kind of "mileage" do you get with your slicks?

A lot depends on the pressure too. Too high (so it feels more solid when driving at low speeds and cold) can let the center go away very quickly. Slicks should only be at racing pressure after a burnout, and if that pressure's too high you're not using the whole footprint either. I haven't run them in years but I had 29.5x10.5 Firestones and they went three summers of very limited street duty and probably 5-6 racing days and still had a ton of meat on them.