Actually, setting AF to application controlled (which is 4X by default i believe when TexMipFilter=3 in conf.ini) avoids the low fps over water=4 regardless of supersampling settings from my findings, its forcing AF in the nvidia control panel that seems to cause it I think.
Also decided personally that i prefer 16q*aa rather then 32*aa, but its actually hard to see the difference...... I was running supersampling =8, but 4 seems to do the job, and when i tried to rip some footage with fraps, 8 was a setting to far, despite being ok in game.
TexCompress=0 also means you have nicer uncompressed textures as well, with a 580, why not.......... Especially if you patch your il2fb.exe with a 4 gig patcher thats been around for a while, for lower systems texcompress will be of help though, but i can really notice the difference in the mid to far distance when looking at maps.
I use this with my 580,
and