Best price / performance crunching rig competition
overclocked to what
1100 core / 950 / 1.18v

1155 core / 950 / 1.17v

1250 core / 1325 / 1.19v
your psu is only 80plus bronze, and looking at the 80plus certification, at full load you're pulling 1025W from the wall and pushing 851W for an efficiency of 83%.

at those clocks and voltages, you're probably drawing around 220-230W on the 7970s, and around 125W on the 7850. so your GPUs are probably drawing roughly 575W.

factoring in the 790W you've measured from the wall, at 83% efficiency measured above in the 80plus certification, your system is drawing 655W. so the GPU power estimates there are probably pretty close, if not a little bit inflated.

your system power supply is able to sustain 851W output, so you have plenty of headroom for your current load. you should only be concerned if you start drawing around 1000W from the wall.
Just rechecked my power reading at full load and its 730 watt.

The reading is using a device that plugs into the wall socket. So I should be able to go to 950 watt from the wall reading?
at 850W you will be drawing 1025W from the wall. and your psu is capable of sustaining 850W output. see the 80plus certification for your psu.