what is on the new tires is the max inflation you could go to if you were trying to carry the max amount of cargo possible.
If your 265 stockers ran good at 33-34 psi, the larger tires would be about the same at 30 psi since they can support the same load at a lower pressure. I find that over inflating wider tires just wear the centers out of them too fast. There might be a bit of trial and error, but 28 psi is where the low pressure alarm sets off at.
The "Chalk Line Test": Draw a heavy chalk line across the tread of the tire. drive slowly forward in a straight line for a few revolutions of the tire. Get out and observe the wear pattern of the chalk. If it has worn away evenly, then the inflation is correct. If either the edge or center of the line is worn first, then the tire is under or over inflated, respectively.