Depends on your weight. To get the shocks to ride the best you should use the air pressures to set the ride height you want. Then they need to be revalved to match the pressure and your riding style. The valving should control the compression and rebound funcions, not the spring. The spring rate (air pressure) should match the valving or it will not be completely right. That is one thing that is kind of a misnomer about air shocks is that they are instantly adjustable for everyone, but they really are not. JT at Performance Fix Racing (406-587-7223) could help you out if you want to go this way. He does good work and is good to deal with. I think it is about $320 to have all four shocks serviced and revalved.
If you just want to adjust the pressures, then start at maybe 65 front and 140 rear and just spend a day changing the setup until you find what you like. Remember, only change one setting at a time. Otherwise you will never be able to figure out what front shock pressures, center shock preload, and rear shock pressure you prefer.