As far as eyefinity goes (6x1080p), which GPU (in 3-way SLI/3-way CFX) would work better, the AMD 6970 or the GTX580? I know that obviously the 580 is more powerful, but I'm not sure whether or not it's as well suited for eyefinity as AMD cards are.
With resolution's like that your going to want as much VRAM as you can possibly get.
Of Course the 6970 comes stock with 2G of memory but their are 3G versions of the GTX580 which would probably be the best.Of course all GTX580's come with a hefty price tag but if your buying 3 of them you obviously have the extra money to get the 3G versions.
Even a 6990+6970 is faster (and a helluva lot cheaper) than tri-sli 580's. The Nvidia cards just scale really badly in comparison but I agree the 3GB versions could win at extremely high 6-screen resolutions due to the memory.
This isn't for a real build, just a part selection competition, to see who could pick the most overkill build.
Although after seeing some 3 monitor eyefinity setups recently I'm somewhat persuaded to maybe look into buying a couple extra monitors when I upgrade from my current 1600x900@60Hz (5ms refresh) resolution to 1080p@60Hz (2ms refresh).