If you are going to drop the money for 3 GTX 580s i wouldn't even consider an AMD build. A 2600k isn't even an ideal choice due to the limited number of PCI-e lanes on Sandy Bridge chips, but on a board with the NF200 chip to give it extra lanes it would work out well, just select your motherboard carefully and it will do fine. Even though AMD chipsets like the 990FX have a lot more PCI-e lanes, i wouldn't consider using an 1100T to power that much graphics, bulldozer chips are pretty much a bust so the 2600k or one of the new sandy bridge-e chips are the only CPUs worthy of a set up like that.
I really love AMD, I would like to rin the 8150 but it just costs too much for the performance right now. 980 or 1100t should push it, over clocked.
2700K is a no brainer.
Not a chance in hell I would pay $1500 for a SB-E setup)CPU and available mobo).
Even the K processor is $500 and it isn't that much faster than the 2700K Plus it produces a lot of heat and uses a lot of energy.
But again, I would prefer AMD. Just not sure the minimum CPU I would need to push them.
Brand preference is silly, prefer for a reason not just because you do.
Anyway, its a $1500 graphics setup, i wouldn't consider using ANY AMD processor for that setup, the $600 for a 2600k and a board with the NF200 chip are worth it to make sure you actually make the most use of your $1500 in graphics cards.
And if you are preferring AMD simply because you feel like helping the underdog, dropping 1500 on nVidia graphics doesn't help them so at that point you might as well just go intel and get the better performance. Im not an intel fanboy, if you look at my config you will see my current system is a 955 with a 4850, but right now if you need raw CPU performance (3 580s does) no AMD setup can compare to a 2600k especially when OC'd.