Are they actual slicks or are they the Goodyear DOT GS-CS racing tire? If they are the DOT racer, as I recall from when I tried them, about 30-35 cold is in the neighborhood (depending on your camber and suspension settings).
I start my F1 stockers at 32 or 33psi and they get up to around 39psi. Car seems to tighten up and feel good around 39psi. Careful on your first lap as it will be pretty "Squishy"!
The best thing you can do is go to radio shack and get a little temperature gauge - the IR touchless type. They make a nice little one for around $50. Link to gauge
You take readings at left middle and right sides of the tire immediately after returning to the pits (Ideally someone checks them for you just after getting off the track). If you are running optimally, the temps should be the same across the tire, meaning that you are using the entire tire effectively, right? If you see the center temps lower, increase pressure, if center is higher, decrease pressure.
If you see either of the outside temps higher than the other two, this speaks to your camber, and can help you set an ideal camber.
33 front 32 rear and I end at 40 hot on them all. It was in the 80's last time out. As Joe said bleed off after session but just before you return to the track. They will lose pressure as they cool and if you do it right after the session rotors and rims are still hot. It will take you more than a few days to take full advantage of the tires performance.
When I first got mine I was told mid 20's but I found out the tire construction has change since the advisor had run them. I did try it at first and it doesn't work for me.