I'll just say that FEAR runs fine on my PC, which is a AMD 3700+ overclocked just like yours, with a 7800GTX which is similar to yours, and a 24 inch widescreen. The game runs fine on max settings with full AF, as long as I keep AA and soft shadows off. You could try putting in another stick of RAM. RAM really helps in FEAR, i've found that 1.5 GB helps the room-to-room stuttering, though you may need 2GB if you have a messy computer with lots of stuff in the background. I never have anything running other than video and sound drivers and some IM programs so 1.5 is enough for me.
Wait a sec, you overclocked a 3700+ to 3.3GHz????? Holy crap!
Thing is, the PC could run it fine before. In the stress test, 100% was over 40 frames per second before, and the only change was the monitor. Not to mention the time it ran fine earlier. It's strange.
Edit: Oh, about the 3700+ - Sorry about that, I'll edit my original post, it's only at 2.31GHz. Must have been a typo at first, and then I just wasn't paying attention to what I was saying! Baaaad. Bonus points to the man paying attention!