If you still play those older games, just stick with the X1800s. If you want to play Crysis, they should still suffice. I'd say wait until the Geforce 8900s/Radeon X2950s come out, or maybe even Geforce 9/Radeon X3k series.
Keep your system, should be rocking what you're throwing at it, especially at 1280. You'd be much better waiting until a games comes out that really needs more power, and by that time you'll be able to make a larger step up on your next upgrade.