As a fellow G&G owner I know a but about the gun. Like luke213 has said, definitely use a MOSFET if youvare running a Lipo. A simple upgrade you can do is a motor upgrade. You can get an awesome motor for around $55.00. Use a high torque over a high speed motor, or if willing to spend a little more a balance motor (high speed and torque). A good motor upgrade will increase your ROF as much as 6 RPS. That's a noticeable difference. It also should give you better trigger response. The hop up you should have no problem upgrading. Th G&G stock inner barrels are quite nice as it is too, not quite a Promethius (by Matrix) but still gets the job done. Unless you have the EBB gearbox, upgrading the internals shouldn't be any different from any other V2 gearbox. There are so many ways to upgrade your gearbox to increase ROF that I will not bog you down with text but, I will provide a video.

I have a stock G&G GR16 (EBB M4), it's been running solid ever since I've had it. (Battery: 9.6v 1600mah) One eveing I was shooting it off my back porch into the would to re-adjust my hop up. I noticed the motor grip was warm so I decided to give it  a rest. Temperature Outside: 55 +/-; shooting for about 10 minutes, not consecutively. The next day I want to my friend's house to do some 1v1 in the woods when I noticed my motor was warm again and I could faintly smell a burning smell. I immediately put it on safety and took out the battery and mag. Later on I ran the motor out of the grip and it seemed fine. I'm not sure if this problem will go away over time or I need a new motor. It's fine if I need a new motor, I just want to know whether I can keep using my current motor without damaging other parts. Also, would I need to re-shim my gearbox eith the new motor? I plan on getting the Lonex A1 Titan.