well the HS gears won't help your situation if you want to reduce ROF. A high capacity battery can supply high current without much voltage drop so your motor will crank out the torque required to spin HS ratio gears.

ouch, HS gears and an aluminum piston....
considering the polycarbonate pistons are just as strong, if not stronger then the aluminum pistons, and considering the aluminum pistons are prone to problems...

high speed gears are not designed to be used in anything over a stock gun.

Standard ratio gears
8.4v
polycarb piston