I use 30-35 on the road. 20-25 on the trail. 8-12 in the sand. If you go to the beach or the dunes you won't notice a difference if you keep your pressure above 20. Just don't be an idot and spin high speed cookies. (Unless you want to bust a bead or have sand blow out of your vents for months At low pressure I only use 4x4 for hill climbs. Oh and if you have an OR do the e-locker mod and rock 2x everywhere.
I wouldnt air down bfg at's in the 265/75 r 16 size any lower than 20lbs. I had mine down to 18 or so at Rouche Creek and it was way too low, almost poped the tire off the rim. 20 to 24 or so is perfect ive found for pretty much any condition.
Mark, I run 15psi with my 285/75R16 BFG MT's, you should be able to go MUCH lower than 20psi.
Rule of thumb is to air down until there is a bulge in the sidewall. If there is no bulge, it's not going to really help much.
As for what pressure to run on the street. Do the chalk test. Take a piece of sidewalk chalk, coat the tread of the tire from sidewall to sidewall in about a 12" section. Take the vehicle for a short ride. Look at the chalk and see where it's wore off. If it's rubbed off even, then what ever pressure you are running is good. If it's rubbed off on the edges, but not in the middle, your pressure is too low. If it's rubbed off in the middle but not on the edges, your pressure is too high. It might take 2 or three times of doing this to get it right. I usually do one front tire and one rear tire with the normal amount of weight in the vehicle.