Acutally MVF does not support 3 way SLI.
This was confirmed by an asus rep earlier on these forums (around the time i was shopping for a board i started asking these types of questions)
For SLI to function it requires at least an 8x lane, Ivy bridge supplies only x16 lanes, which support SLI in x8 x8 only.
3 cards on an MVF require a x8 x4 x4 config which does not work with SLI (even with pcie3.0). Crossfire does run on an x4 lane so he could run radeons, but certainly he cannot do 3 680s on that platform. His only option if he wishes to keep his cpu and stay on z77 is to get a maximus V Extreme (which lacks audio and isnt well suited to gamers generally), or go to some other non-rog board (such as the sniper).
This i typically where i chime and and remind people that building a 4000$ computer on a 'mainstream' platform (z77) is a mistake. You are severely limiting the potential of the system. 690's in SLI almost never makes sense, because for 3 screens you'll need 4GB which it doesnt provide, and for a single screen, 690s in SLI is tremendous overkill.
X79 supports 40 lanes directly from the chip which means x16 x8 x8 x8 is possible without a PLX chip -- this is the reason why the rampage IV formula is such a great choice... it allows for 3 way or 4 way SLI, and no worries about needing to fit an audio board in since supremeFX III is quite nice for audio.
I recommend you return the chip and board, get an i7 3820 and a RIVF, then get your 4 4GB gtx 680s. It will cost nearly the same and you will love the platform.. Or if you are not in a hurry, wait until summer and get an IB-E chip to go with this system. I doubt haswell is an option for this build for the same reason that regular IB falls short -- lack fo pcie lanes.
My current build is a RIVF + 3820. Hands down the best computer i have EVER owned.
Motherboard Asus ROG Rampage IV Formula x79
CPU Intel i7 4820k Ivy Bridge-E @ 4.6ghz
GPU(s) 3 WAY SLI -- EVGA GTX 680 SC Signature (2GB)
Displays 5140x1050 @ 120hz using 3 x Samsung 2233RZ
RAM 16 GB 2133mhz G.Skill RipJaws Z
PSU LEPA G Series G1600-MA
Case Cooler Master Cosmos II Ultra
Storage Vertex 3 256 (Games), Intel 320 Series 128 (OS), + 4TB HDD