You need to give us an example of the output speed, so that we can estimate the torque on the gear (rotational speed × torque = power). Also, what limits the torque on the gearbox (most robots reach an upper limit when their wheels slip, but if there's a braking mechanism, it must be considered)?
As an
estimate, look at something like
this from
SDP/SI. If you mount it rigidly enough, it should withstand typical use in any of the three gears, assuming the DeWalt and CIM are configured per the NBD whitepaper.