The stock 90 springs and FPS are fine so are stock hops when set right.
If you feel the need to put a stronger spring in a quality 90 spring will give you 330 + and a 95 will push you on or just over the 350 mark with a 100 spring mostly well over.
Every gun build is different and FPS will vary with springs and spring manufacturer also the replacement springs are slightly longer than stock springs that come.
I bought a selection of springs from 90,s to 130 to start with and tried them all and with my Specnas 90 and 95 are what work for me the one with 95 spring chronoed at 366 yesterday so could not use it. The gun had been set up exactly at 350 with upgrades but due to warm weather now shot 366 so be aware FPS can climb as well as fall. Note it was fun shooting the snipers yesterday at distance love doing that.