I don't have a 7800GT, so I look at benchmarks, and add 5-10FPS to them. According to the latest 7800GT benchmarks, it gets 25-30FPS in FEAR. I know that I get around 60 FPS on this X1900XT (overclocked) though.
The 7800GT is getting 25-30FPS in FEAR on 1280x1024 resolution with 4xAA and 16xAF.
I'm not saying anything, thats what the benchmark says. I actually add a few FPS to benchmarks, since they're usually overly dramatized and get lower FPS than reality.
The X1900XT, in my personal experience, gets ~60FPS in FEAR on 1280x1024 resolution with 4xAA and 16xAF.
The point being, that the X1900XT is not only meant for high resolutions, but its just as effective in normal resolutions.