Ran Thunderhill last fall, it was easily over 92 deg F ambient. Started at 40 psi hot on PS2 stock 18s, got them down to 38 psi hot after couple sessions and stuck with that. Did not get significant shoulder/sidewall wear, so I probably could have gone a little lower.
Ran Laguna Seca this past Wed, cloudy and passing light showers. Started at 40 cold and pretty much left it there as I didn't run very hard in my sessions and was not gonna chance testing the limits in varying cold/wet conditions.
Whatever temps you decide at, always look at your sidewalls to gauge how much deformation you are getting and adjust (small increments!) as necessary.
revster :: 08 e90 M3 jerez/black/carbon