I used to be in your boat. In fact, for most games I am. So when I was configging Crysis after first getting it, I set it to 1680x1050, put the visuals on medium, tweaked a couple things (still was only around 35-40 fps). I figured, this will work fine. But just for a lark, let me see what the game looks like with all options on high....
After seeing what I was missing, I made the choice that it was worth it to me to run the game at 1920x1200 with all settings on high (shadows on medium at certain points) and lose 15 fps simply because the visuals were so pretty that I didn't care if it felt sluggish. And honestly, 25 fps in Crysis feels like 50 in most games. It's like the developers knew what it was going to do to peoples' computers, so they designed it to feel good even at low FPS. I can't explain it, you'll have to see it for yourself.
Multiplayer may be a different story. I like to have high FPS in multiplayer because there's not really time to stop and enjoy the visuals in the middle of crazy firefights (I haven't tried Crysis MP yet, so I don't know if that's an accurate description, but you know what I mean). However, in single player, where taking things slow and enjoying the technical marvel of the graphics at my own pace affects only me, I will sacrifice speed for beauty. And it is so worth it. I have never seen a better looking game.