Originally Posted by Blacklash
The GTX 280 is most useful @ 2560x or if you want to pile 16x AA on the games you play @ lower res. An overclocked GTX 260 offers a lot of stiff competition to a GTX 280 @ 1920x and lower. The same may be said for the HD 4870. The 4870 sometimes falls down in min frames and that will equal to a rougher gaming experiences. You'll feel a drop to 9 much more than you will one to 20-22.
If you're lower than 2560x and you think the GTX 280 price is a bit much for you, try a GTX 260 from a company that supports user overclocking without voiding your warranty, like Evga or XFX.
So good reasons to have an overclocked GTX 260 or 280 besides solid average frames might be; no worries with multi GPU stutter or bugs, and solid min frames. Hard crashes to FPS below 20 you will definitely feel in game play.
IMO for 1920-2560x an overclocked GTX 260 is the best option for most.
Those are only because you have them to the point that 512mb isn't enough, it has nothing to do with the chips performance, really. Play NV damage control all you want though.