Complete FUD. I run 3 24 inch screens 5760x1200. Obviously not any real issue with vram limits.
Secondly, the difference in the performance of the 570 and 580 is quite low in terms of fps at that resolution. There is no reason to drop an extra 150+ dollars on a 580.
Here is my source:
http://www.hardocp.com/article/2010/12/07/nvidia_geforce_gtx_570_video_card_review/8
Also owning two 570s helps. Notice how the 580 gets 3 whole more fps in F1 2010 at 2560x1600 8xaa 16xaf. If you pay 150 bucks for 3 fps you have too much money and there is no reason to read the thread just buy as much of the latest hardware as you can and enjoy.
Civ V gets 7.6 more average fps but judging by the graph it is still quite choppy and fps in Civ V is fairly meaningless as you need no reaction for the game.
Metro 2033 2560X1600 AAA 16xAF wow the 580 is 22% faster here... too bad by the time you reach a game where it makes an impact both cards really cannot play the game comfortably at these settings. IMO you will need to turn off AAA on both cards which will lessen the gap between them. Therefor once again I feel the 580 is a waste.
http://www.tomshardware.com/reviews/radeon-hd-6970-radeon-hd-6950-cayman,2818-9.html
6950 actually gets less frames at this resolution in this game
BFBC2 Again both cards are really going to need to go to 4xAA for the game to become playable.
http://www.tomshardware.com/reviews/radeon-hd-6970-radeon-hd-6950-cayman,2818-12.html
Again the 6950 actually gets less frames at this resolution in this game.
For most situations a 570 and 580 @ 2560x1600 are going to be playing at the same settings. In some instances it is possible that the 570 will be just at the edge of playing at a setting and then the 580 will be able to turn the setting up a single notch.
I suppose it comes down to your personal calculated utility. However I do not see any merit at all in your claim that he should consider a 6950 as it performs worse at his resolution. 6970 and 580 are worth about 3 - 8 fps on average at that resolution with settings cranked to 8xAA. Honestly on a 30 inch screen the difference between 4x and 8x is not that easy to see in game play. For the one or two games you will during ownership that will allow 8x vs 4x I think it is not worth 150$. Question for the OP is do you?