The ram isn't just for Resolutions, I mean look at Crysis 1 Assasin's creed, etc they stress out cards alot even at 1280x1024.
To OP, if you are looking into play games in the future then the 260 GTX would be a good choice for your lcd monitor, and for high textured games.
But if not, then like ranger said the 4850 would do you well , adn its pretty cheap.
Even a 8800 GT could do alot but only for current gen games, as for new games, unless you sli the cards, they might not perform the way you want them to.
Personally if your gaming go with the 260 GTX or the 4870, or better yet wait for the 260 GTX revision, which should be faster than the 4870 or might help it be onpar with it.
nothing to rush now, unless you really must!