I base tire pressure strictly on how the tread is wearing. If the center is wearing, I let more out, if the sides are wearing, I inflate them.:17:
I have gotten to the point where, on both my truck and our OBW, and every other vehicle I have owned over the past 30 years - the tread is nearly perfectly-worn across the entire width of the tire.:17: In the OB, it has meant having to run them several pounds below what the door says (I run about 28F and about 26R).
In my work truck, that tells me to put 60 in (the tire sidewall states 80 PSI Max with full load), however that is with a 3/4 ton full load (the truck is a 2500). Lately, I have been running 38 pounds all around. The truck handles perfectly on sharp turns, no tire noise at all, and the ride is much more comfortable as I am not feeling every tiny bump in my bad back!:17: