25.2V is the max volatge, 22.2V is the nominal voltage. No one refers to a 6S pack as a 25.2V pack. I would think youd know this as long as youve been in the hobby
Spur and motor pinion. Those are generally the only gears you can change. not many kits (if any) have a choice of transmission...
Technically you can run up to 6S (or 22.2v) LiPos. The motor is the limiting factor here, at least in terms of the electronics. The suggestion to run it on 4S is probably a sound one although if you're not afraid to break parts and try to rebuild it stronger than before then your electronics can...