I would go with the Maximus V formula!
If it isn't a budget bust, you might want to consider twin GTX 690 (2 bined 680 GPUs on one card) to drive those monitors. I am not really sure what kind of frame rates you can expect to get with either direction, but 11,318,400 are a lot pixels to push. I think this is the only supported way for you to go 4-GPU SLI with Nvidia.
It isn't clear what alternative board, to the Formula you mean. You said Maximus IV Extreme and X79, Maximus IV Extreme is a P67 motherboard, the Maximus IV Extreme-Z is a Z68 board and the Rampage IV Extreme is an X79 board. All of these other then the Formula are Sandy Bridge artitechture boards, which means PCIe 2.0. The Rampage is Sandy Bridge-E a different socket (2011) from all the others and doesn't have the onboard GPU, which means no quicksync. The Maximus IV Extreme doesn't support the onboard GPU either, even though it is on the processor. All the sockets and similar names of boards can get quite confusing.
🙂There is also the Maximus V Extreme, which would allow 3-way SLI, has PCIe 3.0 and is built on the same Intel chipset (Ivy Bridge Z77 and Socket 1155) as the Maximus V Formula. It is also the top end of the Maximus V line. The Formula has a better audio section, a combo water block/heatsink on the VRM capacitors and liquid nitrogen cooling support. The Extreme has some additional over clocking features that are focused on hard core OCers (but lacks the liquid nitrogen support) and has an ASMedia PCIe 3.0 controler to allow more PCIe 3.0 slots. The later is the reason it can support a 3 Card SLI system. One more note on the Formula, it officially only supports 2 Card SLI, you might be able to get 3-way to work, but it wouldn't be supported.
This was a lot of information in one place, I hope I didn't confuse things further. Their is a simular build log to what you are discussing here:
http://rog.asus.com/forum/showthread.php?20477-A-new-ROG-build......parts-and-comments-at-this-stage
