Definitely a good quality hopup + rubber.
I guess sorbo pads or something (not sure if those are only for AEG's though).
That's all that comes off the top of my head, but I've heard of people dumping a lot of cash on their gun to make it a game worthy sniper rifle. Also chances are no ones going to let you run a hot gun on the field not knowing who you are. You have to be trusted, safety oriented, and proven, so you'll likely be running a 400 FPS gun rather than 425-450.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE