If you ask me, Prometheus Soft. I know that someone was also recommending the Guarder Clear/Black too.
IMO if you really ask me 10-20 FPS isn't that much but if you really want to upgrade it then I've been told that Modify isn't that bad and the S100 (I believe it was rated for 370-380 FPS) or S110 (slightly shy of 400 FPS) is probably the ones you want.
I'm not sure about the switch assembly though, you'll have to wait for someone else to reply.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE