as far as the original question.. it's a squad automatic weapon, which means you will be putting plenty of rounds down range towards your target.. i would say you should run it stock, dont screw with the gearbox and you wont run the risk of pre-maturely stripping something or some other mishap. obviously it is too late for that, since you have already installed the stronger spring.. echo-1's shoot pretty decent out of the box, use some heavier ammunition if you want more range..
another way to boost your power output without straining moving parts; you could have thrown in a tighter barrel (which you did?), and an upgraded hop-up system+bucking, but make sure you are using high grade ammunition, and a high-grade barrel. and that wont always give you a boost, if your previous bucking had a good seal then you might not see that much of an improvement (as far as FPS goes, since it seems that is what the concern is here).
other upgrades? well, there are a limitless supply of cosmetic parts - including but not limited to stocks, grips, bi-pods, magazines, slings.. the list goes on.. asking for what upgrades you can put in is an extremely vague question, almost every part can be changed out/upgraded
but back to my original point regarding spring upgrades in this type of rifle; as a support gunner, the last thing the other players you are supporting need is to have a gap in the suppressive fire you are providing because your upgraded rifle jammed up in the middle of a movement... that's what i would say regarding upgrading your rifle
the last game we were at, our saw-man had a magazine mis-hap and ended up having to hike back to the staging area and secure a new rifle. that is inconvenient to say the least
again, you shouldnt upgrade just to upgrade.. if the rifle is functioning properly, then just use it until you are forced to replace/upgrade something..
