Over-inflating... how much is to much?

[rgathright]

I have a set of Firestone Destination A/T 33X12.5RR15's on my Jeep.

I filled them to 37PSI last night. I have seen discussion on the forums of people who say you can overinflate... what would be a safe number for these tires?

P.S. I know they ruin my fuel economy but replacing them would cost at least $400. The cost would not equate into more savings at the pump.