I beg to differ. Aside from the fact that I don't believe it can even be reasonably done at all (without massive modification to the chassis and drive train, to the point of no longer being recognizable as an X-mod), I don't think it's needed. Hell, even the electric VW we built in high school had a 4 speed, but we only ever used second gear. The motor can handle very high RPMs, can't stall, and has peak torque at 0 RPM. And here's the kicker,
there ain't much space to work with.
Once you consider the
complication of the typical RC two speed set up (and this design is an automatic shift, no tx/rx needed), and the dubious improvment in performance (in this scale), I seriously doubt this would be the greatest thing you could do for an xmod.
Hypothetically, if you did it, I'm sure performance could be improved. Significantly? I'm not so sure. But I honestly don't think it can be done in an xmod.