After 3 days and 10 sessions at Buttonwillow in February on PS2's in a 06 SRTC, I'd start at 32 - 34 psi cold and look for about 38 - 40 psi warm. This pretty much follows Mark's recommendation above.
The side walls seem a bit soft on the PS2's and they tended to roll under a bit with lower inflation pressures. It was very warm that weekend, 85 to 90 degrees F and Buttonwillow is a rather slow, twisty track.
Hope this helps get you to a starting point. Adjust from there.
Dan