I am currently contemplating a monster build with ASUS Crosshair Extreme, 1100T (or rather bulldozer) and 4x MSI 6970 lightning. These beasts eat 420 W each, so I need two PSUs
My idea is to run 3 of the GPUs off an OCZ 1250 PSU, which actually has enough 8 pin connectors and run the rest of the box from and 850 W PSU. Since i gather that a GPU that ahs now power on the PCI-E connectors does simply not show up in the system my thinking is that i could use the system with the 1250 W PSU powered off for general computing and shutdown, switch on second PSU and power on again for gaming. It will take a reboot, but should rather majorly save my energy bill.
Planned Displays are 3X 1920x1200 in portrait since you were asking
Not even at extreme resolutions like that you'd see a real benefit from 4 cards, it's a huge waste of money, 3 cards would scale pretty well at those resolutions though, but adding a 4th one would hardly be a 5-10% improvement, and that's only on benchmarks as the vast majority of games won't even see an improvement at all, and you could run 3 card off a sinle PSU too.
I've seen conflicting opinions on that. I saw one guy who actually had 4 GPUs comment that it actually scaled pretty well. and two PSUs have the advantage that I can run it like a non gaming rig when I don't game
Even if 4 card did scale well, they don't. Most games wont benefit from the fourth card regardless and some will actually perform worse. Three cards is the sweet spot, plus it won't kill you power wise.
Wait you're doing all of that on a 1100T? Wait for Bulldozer or go 2500K. Unless someone can prove me wrong, I don't think a 1100T will suite a 4GPU build very well.
Regardless, I'd go with three cards, see if you're performance is acceptable and then go with another GPU and another card if you really feel you have too, but I don't see it being necessary.
lol, 1100T. Seriously, a high end rig like that will be bottlenecked with an AMD CPU. even 2 6970's would be bottlenecked with that cpu. Intel has them beat by a huge margin at the moment, AMD cpu's are only good for low end/mid-range builds.