OK, thanks. I have the tool box with some stuff in it but altogether I doubt it totals 200 lbs. I carry a bunch of misc stuff behind the seats which probably isn't 50 lbs and that's stretching to the high side. For day trips off road all I'm adding is a cooler and a couple aluminum chairs, maybe a folding table, it still doesn't add up to a hill of beans compared to what you're talking about for loads. So really that all adds up to roughly carrying 4x 150 lb passengers (the "standard") and no payload. FWIW. So, usually, not really much weight added.
The other day I was running 31 psi all around and it drove real nice on dry or wet pavement, felt secure, didn't wander, steering felt good, neither heavy nor wandering, of course it'll probably never feel really heavy with power steering but that's the best I can describe it. And it was good off road. I didn't have any slipping or spinning or sliding.
Where I went I actually had been a good ways up in a Saab Aero (ok, dumb, I know, not much clearance but the front wheel drive gets you there). But it had huge gulleys down the middle of it. Since then it looks like they dumped a lot of dirt on it and it was pretty smooth, some stuff sticking up but a rock sticking up 3-4" doesn't really even come close to clearance. There can be other things like places gravelly and humped in the middle but usually you can find the good place. So that's all good and one would say "mild off-road" but here's the thing it was wet and it makes like a slurry or slime or film of fine mud on top and while I didn't do any tests like I used to do in snow ("how slippery is it?"), it seems that if you are on a steep grade, going up is easier/safer than going down because going up you can just let off the gas and you slow down immediately; going down, if you lose traction, logic tells me you are in for a slide and there's of course no guard rails and lot of places it drops off precipitously so a slide could easily mean you are walking home and probably have a wrecked truck at the least. So I call it then moderate off-road not because of road obstacles but simply the danger of it. I realize I'm wandering the thread here, but it has to do with, what's the grip of the tires on that kind of surface. They seemed good, tread is open enough to not load up with that silty kind of mud. Going down I just go real easy, feather the brakes, keep the speed slow. I probably should have been in 1st (auto trans), thought of that afterwards, might help a little. I did stay in 4x4 going down, not sure if that helps or not.
Certainly if I did ever really load up I'd add air. Sometimes off road maybe I want to air down. Anyway, 31psi might be a bit low if I were hauling stuff or if I were driving exclusively on the highway but I think it might be a good balance all around for what I do, although depending what I see in wear, contact patch, and feel (latter which seems really good right now), I'm not stuck on it. I don't think I'd go lower though unless it was airing down for off road.
I'm still wondering why is underinflated more dangerous than overinflated. I appreciate the help.