G&G combat machine m4 motor? (Airsoft)?

So i'm planning on getting a G&G combat machine m4 very soon and i would like to increase the ROF. I saw on youtube (an airsplat video) a guy changing the motor to a Systema Energy ( a href="http://cgi.ebay.com/Systema-Long-Type-Energy-Motor-Airsoft-/250797374066?pt=LH_DefaultDomain_0&hash=item3a64b03a72#ht_2036wt_905" rel="nofollow"http://cgi.ebay.com/Systema-Long-Type-En…/a ) motor and the ROF was then 13-15 RPS! ( Mehh i think thats good ) And i was just wondering, what motors would work good (Or just as good) ? I have an old JG M4 S SYSTEM with a i think 3000 high torque turbo motor in it (Not sure what it exactly is, don't feel like checking ) and was thinking if that would be good. Also, if i need, there is also a M120 spring in the JG. (Stock spring in the G&G combat machine m4 i think is m100, and i think the stock motor is 2500 RPM ultra high torque motor) Thanks a lot! If you really need, i can actually check the type of motor thats in my JG.