my spec's
i5 2500k Stock settings
16GB DDR3 RAM 1600MHZ
GTX 580 SC 1.5GB
so i notice that anything to do with shadows is major FPS hitter nothing els AA takes hit on FPS but nothing like shadows. water you can have it on very high makes no differences really, when looking at it from low to very high none what so ever. I'm getting well over 60FPS like 70s to low 80s never drops below 60 ever with this settings and visuals are just stunning still there is no differences i find post processing makes it little grainy for some reason so removing it will make image clearer and easier to see stealth people trust me it does... and turn blur off or low anything higher is just bad for competitive gaming having it max drops me to 30 to 24 fps and its only due to shadows nothing els really is huge on taxing the GPU its crazy.. but i find that game effects do take a hit when on very high but visually there is no differences wile playing. Effects are just not that clear in first place to notice it how HD the effects are...so turning it to low will make sure wen lot is going on with huge amount of effects that u get no sudden dips. honestly... there is no fricken differences at all only thing makes differences is mainly post processing in terms of visuals and ofc shadowing.. but honestly.. its super minor... veryyy minor.... we talking like 5% minor...i also find that particles are too heavy just little too much for my liking personally that's just personal preferences
for Nivida users go NV control panel and do the following...