are you serious...
What size moniter do I need for 2560x1600?
around 30" as of the moment. sorry to make you feel bad, but i think at that resolution the gtx 285, even with 2gb would just be adequate, if not struggling.
..so dont plan on jumping to that resolution anymore, else, im guessing that you will again get tempted on upgrading your video card. stay on "full hd" and be happy with ur gtx 285