[Hectic]

I think the real point to make about the 20 fps is that it will have quite literally no effect on your range or accuracy. 100 fps. That'll make a decent dent. 50 fps. Not all that noticeable. 20 fps no effect.
A 285fps TM vsr 10 can shoot further and more accurately than a 400fps stock aeg from China. Because the hop rubber, unit and inner barrel are of good quality. If you upgrade a cheap gun it'll not perform as well as an upgraded quality base. I can attest as my first Vsr10 was a tsd, after putting all my laylax parts into a TM it's a huge improvement in consistency. The same can be said for cheap parts. Buy clone parts get clone results. A higher fps gun will afford you the luxury of shooting a heavier round however in doing so you increase you minimum safe engagement distance "MSED" so it's always a trade off. If you go for the <450fps mark it's the best place to start sniping. You get a good hop up and barrel and some good .36 or .40 bb's and go see what you may need. For most it's a good optic and a good ghillie. The fps of a sniper is not his/her greatest advantage it is patience and stealth that win for us.
I like running with a 300-400 fps bolt action because I can cook it easily, it's super quiet and I can shoot u as close as I would with a pistol lol
And yes you don't want to cut or heat/stretch/temper your spring. Either change spring or use spacers if they are visible for your gun.