Bullit,
I, too, have been autocrossing a number of years, nine in my case. However, my first year with my MSP I campaigned in Street Tire class on the OEM Bridgestones, and I'm glad I did. By midseason, my driving had improved to the point where I was only a couple of tenths behind the leading DS cars on R compounds. As for wearing out the stock tires, I put about 75 autox runs on those tires and they now have 22k miles on them and are not down to the wear bars yet. I estimate I'll get close to 30k miles on them overall. The OEM RE040 Bridgestones are pretty good tires if you keep the car aligned and rotate them front to rear every 5k miles. This year on R compounds (Victoracer V700s), I'm leading my DS class and PAX overall consistently in the top 10 out of 100+ drivers. Some of that is due to the MSP, and some of that is due to an improved driving style that gets and keeps the MSP very near the limits. That's why I recommend to everyone that they run a new car on street tires their first season, to really learn how the car reacts at the limits of adhesion.