pull a tire or go to salvage yard and see what is on the inside of the wheel. I know they put the dimensions there not sure about the max psi. Also check a wheel store and ask. Not sure you will gain anything by going to the heavier tiers as they will weigh more and really not aid in being overweight on the frame and running gear. Whatever if you need to go higher make sure you install the steel valve stems not the rubber ones.
As a last resort send a mail to one one of wheel manuf and see what they say. Arrow makes AM aluminums they might have knowledge on who to contact.