If you have the money for 4x Titans why are you considering anything less than intel's i7 3970X CPU? Frankly I'd like to know how you manage to get 4 Titans onto any motherboard that isn't based on intel's socket 2011 with the extra PCIe lanes needed to feed them.
Some of the really high end Asus boards for socket 1155 and socket AM3+ have 4 PCIe lanes. (sabertooth/crosshair/maximus)
True, but without the extra PCIe lanes coming out of the i7 via the 2011 socket the quad SLI is going to be starved of bandwidth.
Agreed...I would never advise doing it...but you theoretically could fit 4 cards onto 1 board.
I would think 2 titans would be plenty...or if you want "4 GPUs"...then just SLI/CFX 2 GTX 690s or HD 7990s.