[yuhaoyang]

ujiro is right in saying that it's the all around air seal that provides more consistant fps, from the piston and cylinder head to the nozzle, to the hopup unit's seal with the mechbox and mag.
a triggermaster will not crank your gun beyond what is mechanically possible, essentially it can slow down your ROF, but not speed it up.
For light upgrades, I would say a large 9.6, maybe a prommy ms100sp, and a G&P M120 motor, and a modify upper mechbox set (cylinder and piston assembly) the ROF won't be high enough to warrent a sector clip.
if you want to spend more money, add in that triggermaster mk3, maybe prometheus upper mechbox set. BTW, theoretically bearing springguide and piston head should lower variance, although I've never tested it out, I just spent the money brainlessly.
even more than that, well, you're going into the realms of torque up gears, FTKs, and yet more powerful motors.
no matter what upgrades you do, as long as you're not aiming for watergun, I personally stick to a large or mini 8.4, which is plenty.

EDIT:shit my balls, I misread OP, edited to match

Actually, if you want to try it out, give everything a good relube and clearance test, it should drop the variance a tiny bit if it hasn't been done before.