I'm playing with TressFX on, and after playing with it for over an hour, I just can't disable it, the difference and superiority is just to obvious... the hair moving really helps the game to feel more natural, even if it's far from perfect...
I'm playing with FXAA, AF 4x and tessellation OFF, the rest is at the maximum available (like on Ultra), with a relatively low resolution (1280x1024), since I'm using one of the old 5:4 screens, the VGA is some old 5850, tessellation on is just to much... if I was trying to play at 1080p I would probably need to play with TressFX off (or lower a few other things).
TressFX on = 36
off = 57
it's a huge hit, but even with it turned on it's almost always easily over 30FPS