if not already corrected, springs with an S before the number listed are not measured in m/s, for example, an M100 will get you around 330, you are correct, however an s100 will get you between 365-375 FPS. All spring brands have charts in order to pick out the right one, find them, and then find the right spring for your application :)

Also depends on the gun.
A systema M100 on a CYMA M4 might get you 300fps
On a fully upgraded king arms M4, will get you the full 365fps

I had to put a m90 in my m4 to get below 350. The m100 had me shooting mid 390's. Safe bet would be the m90. And jugglez great to deal with

Yes, lots of people will tell you to get an M90 (or equivalent) spring. This allows you to have FPS hovering around the 300-340 mark, depending on the gun, which will usually qualify you for CQB skirmishes and provide a good platform for Field games. It's a Win-Win spring.

yes, lets not leave compression out of this discussion aswell. If your gun has a loss of compression, the spring is the least of your worries, fix your compression problem then move onto a larger spring if need be! we dont want any broken gearboxes or broken gears for absolutely no reason!

Well i just chrono'd my KA today stock im getting 400 with .2, I would recommend the m90- to m95 ... i got a m95 havent installed it yet but fingers are crossed that it will keep it under 350 if anyone else is using a m95 could you tell me what your shooting at

m90 = 90 meters (per second) = ~300fps
m95 = 95 meters (per second) = ~315fps