i got a G&P m120 in my combat machine and it works great. much better than the stock motor. i reccomend on of those.
if your guns over 350 fps, That motor is just causing your batterys to die faster.
Gfiller, Honestly you dont need a new hopup. the gng hop ups are more than capable of what you want.
replace the bushings tho's are crap, same with the gears they use in the CM's, There not too great, Iv had better results with XYT's out of a cyma.
Get your self a good stainless steel barrel, a good hopup bucking and install a 120 spring, While your at it replace the motor, with a Magnum type(High torque/high speed) Or high torque type. and get it reshimmed By a pro. it will be good to go.
and dont go with a masumone spring, Unless you want to pay somone el's to replace it when it snaps in half. I'v yet to see one of tho's springs last more than a month in one of my guns, I ordered 15 of them because of price... heh i wont even give them away there garbage.