Recommended tire pressure is usually written on the tire, some small print.
It really depends on the tire, less rubber between rim and road means you need more pressure to keep the rim from hitting the ground when you hit a hard bump. But that in turn makes for a rougher ride, kind of a trade off with bigger rims though. I would try it at 45 psi and if it's too harsh try 40psi. Remember that incorrect tire pressure can also affect the wearing out of the tire Abd cause scalloping or cupping.
The set up looks sweet though. If your just going for looks and not going off the beaten path I would recommend a 2" spacer lift like the one PRG sells.
I found this from cooper tires, might help you out
http://us.coopertire.com/Tire-Safety/Ti ... ation.aspx