not all do, my friend bought a sniper for 50$ and it shoots 420fps and my brother got shot by it and the bullet inbedded in him. it was really funny
Earlier I said that snipers were the only good spring guns. My friend mods his sniper (He got a nice trigger that shoots if you barely touch it) and got some POWERFUL springs for his gun. The first one he got was pretty powerful, he was roostering it and it jammed, so he sets it on the ground a little to hard which caused the trigger to move and he shot himself in the ear. It was embedded in there for 4 hours before he finally got it out. He got one that was even more powerful, and when he tried to rooster it, it broke his gun. But overall, power doesn't matter when you get rushed by an AEG and have to rooster a rifle after every shot.
Don't get High-FPS guns just because you want to hurt somebody. It takes the fun out of the game, and some parks have a limit to how high it can be (typically I think it's 350fps). Get a nice, sturdy, accurate AEG.
350 is a good FPS to get. But High-FPS guns are the way to go if you play how my friends and I play. We got tired of lives (Everyone cheats), CTF got boring, so we started playing pain free-for-all. Pretty much, you can get hit as many times as you can take. The people with the powerful guns started forming alliances and dominating, so everyone else started getting more powerful guns. At first, everyone had spring pistols (180-200 FPS) and pump shotguns. We've elevated it to M4s, G36s, AK47s, Snipers, CO2 pistols, Gas Mac10s, etc, etc. (All those guns fall into the 350-420 FPS range). We've pretty much maxed out on how powerful the guns get without getting too expensive, now we are going for either accuracy or rate-of-fire. I guess we could be called "Hardcore". But yea, if you don't by the P90, get an M4 with about 350 FPS, pretty cheap, lots of parts, highly supported.