Properly undervolted 7950 (I run mine at 1.075v that gives me 630kH) draws just under 200Wa. Your system is using between 100-160wa.

In one of my systems I run 3x5850 and at the wall I have 500 wa consumption.

You should be able to run comfortably 3x 7950/7970 or 4 older cards at efficient PSU utilization.

Kill-A-Watt is awesome tool when optimizing your miner settings. Remember, you want to undervolt and overclock your GPUs.