I use the Element M4 hopup unit with a Prometheus rubber a long with a Madbull tight bore barrel.
Got the unit from CapitalAirsoft and the other bits at Airsoftparts.
Eventually I am going to swap things out and get a Shredders concave spacer in there, but for now that combination works great.
Glad you enjoy it!
Maybe you should get some German kit and come out with the cool kids