The i7-3820 only draws 88 W full load? I know 130 W is TDP, but shouldn't that be used for a worst case scenario?
I was hoping to overclock as high as I can go with the i7 3820 at 1.3v to be safe. The 7970s will be overclocked as far as possible with stock or near stock voltage, if possible.
So will 850 watts with an 80plus rating be enough with such a modest overclock?
And what little money saved on an i7-3820 over the more popular i7-2600k will be spent on the platform. A high end 1155 board is not much cheaper than a decent X79 2011 board. The i7 3820 may be partially locked, but I've seen others get them to at least 4.5 GHz, so I'm sure with a decent X79 2011 board, I can do the same.
With the i7-3820 running at 4.5 GHz @ 1.27 Vcore behardware.com measured a 135.6 Watt power draw on the +12V CPU power connector. That includes the power loss in the motherboard's CPU VRM power circuit.
I would allow at least an extra 85 Watts on top of the 525 Watts when running Furmark for the two overclocked Radeon HD 7970 in 2-way CrossFire mode.
A card like the MSI Radeon HD 7970 Lightning can draw up to 348 Watts when overclocked to 1170 MHz Core/1600 MHz Memory and running FurMark stress testing in ht4u.net's review of that card. In TechPowerUp.com's review of that card they measured 379 Watts for that card while running FurMark and the card wasn't even overclocked. Running two cards like this in 2-way CrossFire mode is slightly less than double that.
If you want the power supply to power the system under the worst case scenario, then you should be looking at something like the Corsair Enthusiast Series TX950 (CMPSU-950TX) or better.
Your initial post suggesting a 1050 Watt may very well be the better fit.