Some very good info here from mightyya, radiation joe et al. The PS Cup is for either:
1) crazy hardcore street drivers
2) club racers / lapping day participants
3) occasional track drivers
When winning is paramount on the track, use BFG R1, Hoosier or other DOT slicks.
If you're not a madman on the street, PS2 or similar will give you all the grip you need, with more life and better wet traction.
But if you only go to the track occasionally, and don't want to have an entirely different setup, or if you run on the track often in a less competitive environment and want a race tire that will last, the Cups are perfect.
I have accepted a new position at Tire Rack and am no longer in the sales department. firstname.lastname@example.org
is available to assist with M3 questions.