The biggest advantage our team has with a smaller wheel size is the height difference; the smaller wheel size allows us to fit under the Ladder easier. I would recommend gearing down a 600 rpm motor (blue cartridge) to 450 rpm using a 36:48 gear ratio on 3.25 inch wheels. This is what our team uses, and it works well for us.
Check out Catalogue of Drive Gearings, it’s really useful in choosing a gear ratio for your drivetrain.