The PSI in the bump stop is variable depending on the weight of the rig and what you plan on doing with the rig... The bump stop manufacturer should be able to tell you what the force is at what preasures...
but something like this:
100 PSI 150 to 450
200 PSI 300 to 850
300 PSI 450 to 1300
Mine are 2" kings, and I think they're set at about 85psi now. I've experimented, jumped it, drove the piss out of it, etc. If they bottomed out, I added a little at a time until they stopped.
Just an update to the thread. I set mine to 150 psi last week. I wheeled up at Evans with them, the front end feels a bit to stiff at initial impact just cruising down rocky roads (the bumps sit only 2 inches or so off the axle) so I plan to drop them down to 125 psi and try that out.