I would run them at 28psi cold, and keep releasing air to keep them at 28psi as they heat up throughout the day.

At least that was what Leigh advised when I was racing for the RMS team last season, and it did make a difference in grip levels. I used to run them at 35psi, and then 34psi, and then 32psi, and then I asked Leigh what pressures he ran, and was shocked to learn he ran them at 28psi.

Obviously it depends on your driving style, what tyres you using and how your car is setup I suppose. 28psi worked for me, when I had Tein HA coilovers, a multitude of swaybars/bushes/etc, Bridgestone RE55S hard compound R comps.