I often have thought about changing the wheels on my board. Larger diameter ones would make it go faster, smaller ones give it better torque going up a hill. Stoked LA give a very good overview about wheels for your long board.
It seems the 78A PU 90mm wheels that come as standard on my Volo-e longboard are a safe bet. Though, interestingly Stoked LA advise that going over 80mm diameter can give risk of bending the standard 8mm axles of a skateboard truck with aggressive riding (but I think that is more to do with non electric boards)

Stoked LA present all aspects of wheels that should be considered by a skateboarder: diameter, width, durometer wheel lips etc. Who would have thought there would be so much to know about wheels?