Depends. I can usually get away with most settings maxed out, usually keeping the AA around 2x or 4x and the AF around 16x. Keep in mind that AF really doesn't impact performance by much...and at 1980x1080, do you really need more than 4x AA

?
The only two games that have really challenged my rig so far (that I've played) are Metro 2033 and Skyrim.
It's funny because I've been using the same rig for around 3 and a half years now, and while I have considered upgrading, I've realized that not only are there only a couple of games that I can't max out, but even if I can't, I really don't need to play them that high.