6800 won't handle the res.. may be playable with everything at lower settings (lower texture quality, no aa, very little af) if you can stand the eyesore and don't mind dipping below 30fps.. most monitors can interpolate lower than native res (tho the image suffers) and you'll like want to run thngs at 1280x900 or lower depending on the game..
6800GT is almost in the same boat, but not as bad. older games will be okay for the most part, but you'll still likely need to make many compromises in the are of image quality (i just took the 6800GT out of my wife's computer a few days ago, and it had problems keeping a decent framerate in WOW at 1440 unless i turned texture quality way down with everything else at low-med settings). decided to stay with agp a while longer and installed an x1950 pro, and in many cases it's 2x faster even when running higher settings than the GT. don't get me wrong, the GT has served us well for 2.5 years, which is remarkable for a graphics card, but it's age definately shows at higher resolutions with newer games - even games like WOW which isn't exactly 'taxing' on the system (like rainbow6, for instance).