On my 1/2 ton truck it lists the RGAWR with p tires at 35 psi on the door sticker. The rating was exactly what the tires were rated for. I upgraded to e tires and gained some more payload. Now how much is a good question which I really don't know as the e tires were good for 3500 lbs each but I know the axle wouldn't take 7000 lbs. Although I'd be willing to bet I gained at least 200 lbs more capacity.
As far as loosing the mattress for an air one waking up to a flat mattress at night does not sound like fun. Plus if you have to carry an air pump with the mattress you haven't gained that much.
For the AC, do you camp in places with 110 hook ups a lot? I have never camped where it has been available but did add a fantastic fan and when turned on to suck air out of the camper I can open a window in the bed area and get a nice breeze when I sleep.