I'll give an unbiased opinion on HD 4870 X2 vs GTX 295.
Depends entirely on the game, some games the GTX 295 wins, sometimes the X2 wins, sometimes they draw. Although the 295 probably does have the X2 best for the most part, and that's why it costs more.
Anyways, back to the original topic. I agree with AR, a HD 4870 1GB
is enough for 1920x1200. I'm using a HD 4850 512MB at 1920x1600 and I have no problems. The increase in cost from the 4870 to the X2 just isn't worth it for 1920x1200 IMO.
Here's a review of the HD 4870 1GB
if you want to see how it performs.