For larger tires, your tire pressure should be reduced to keep a proper tire profile and contact patch. Bigger tires = larger surface area on pavement = less pounds of truck per square inch of surface supporting it. Psi on the tread side will be about the same as psi inside the tire. Increasing tire pressure means less tire will contact the road, the edges of the tread will lift, and wear will concentrate in the center. Maybe less tire heating, less rolling resistance, less tire flex when cornering, but funny wear pattern, especially if you run stock rims with wide tires. These heavy trucks tend to wear the edges off the front tires if you do a lot of cornering, so maybe a little extra pressure would be good. This is all theoretical, I run 265s and run 270s on my wife's truck.
I agree, I run my tires at full pressure for street driving. I feed my BFG's a full 45 psi load after every trip. I would only consider dropping the street pressure if I saw more wear on the center on the tires. You get better tire life and more gas milage on full tires.
Thanks for all the feedback. I only got around to checking the pressure on my 285/75s for the first time today - have about two months on them and a few thousand miles. They were at 55 psi, so I bled them down to 45. It's always the simple things that jump up and bite you. BigMac