If I were in your position I would do the following:

1) I would rent from a local forklift dealer rather than a rental yard- rate might be higher, but you can specify exactly what you need

2) The forklift dealer can give you the exact specifications on weight distribution at different levels of weight carrying.

3) Given the specifications, you can from there figure out the weight per inch of contact area.

A pnuematic style tire (air or solid pnuematic) has more contact area than a solid press on tire.

A lighter capacity lift will have more loading on the drive tires than a heavier capacity life- at 3500 lbs.