You will only see benefits @ 2560x1600 but lmao even then its not even near from playable lol
If they are around same price +-10$ I would take but not worth more.
And no the 480 will win from a FPS perspective, though I am more waiting for the 5970 4GB which should get more benefit from it at such high resolutions.
I would wait until they OC the card as it may OC less than the 1Gb actually as seen with previous generations.