[suicideneil]

Gearing depends on whether your motor and batts can cope with the current draw- the esc will be fine as it will thermal before any damage is done (famous last words). What are your current motor, esc and lipo temps after a good run? 20 to 25 seems like a rather large gearing increase though, might want to rethink that and go to something more like 22tooth pinion, or a few less teeth on the spur instead (same effect).