[Hectic]

prometheus smooth hop rubber and bridge tenssioner (orbthe modify flat hop)
a good barrel, lotta choices. Madbull, prometheus lots in between, get something good that you can afford.
good piston (lonex makes a nice one) shave off the seccond tooth(the one after the pick up tooth)
good piston head (lots to choose from)
sorbo pad.
if u want u can do a fet (like the merf 3.2) while yer in there to improve trigger response and support an 11.1 lipo.
Thats about it, the stock spring in that gun should alrdy be over 400 fps from what ive read its 420ish and youll prolly go up a bit by improving the piston head.
you could also do the cylinder head and.nozzle too if.ya wanted to.
and you could do gears as well, maybe go 16:1 for even better trigger response.