I just brought up my brothers FAMAS to 350, only changed spring and bushings, PDI130 (which was somehow shooting 400ish) and 6mm steel bushings. Maybe I should have got a V2 steel spring guide and cut the nub off for the famas mechbox. I ended cutting off about an inch from the spring to drop the fps down.
Here's my post of FAMAS problems.
http://www.airsoftcanada.com/showthread.php?t=87781
Goodluck