[asid61]

If it's single-speed it depends on the driver mostly. Can they properly position your drive, and quickly? I would recommend making a system with a number of selectable gear ratios so you can decide on the fly. A vex clamping gearbox with a secondary sprocket reduction to the wheels could work well.
Anything above fps can technically work, but I think we're going with something like 14fps.

The robot + totes is only 180lbs, and you're not pushing other robots (hopefully).