I'd be more concerned about the rest of your gun's guts if you're going for an insane high rof than the motor. I'd suggest at the very least installing metal bushings in the gearbox, and perhaps a piston with metal teeth. You may also encounter feed issues and might require a sector gear clip to help with feeding at high speed.
I'm not sure that a 7.4v Li-Po wouldn't give you a huge increase in rof. An 11.1V would though. That would more than likely give you something in the high 20 / low 30 per second range. Just beware because it doesn't take long to empty a mag like that. You run out of ammo real fast.
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