Our test system is based on a power hungry Core i7 965 / X58 system. This setup is overclocked to 3.75 GHz. Next to that we have energy saving functions disabled for this motherboard and processor (to ensure consistent benchmark results). On average we are using roughly 50 to 100 Watts more than a standard PC due to higher CPU clock settings, water-cooling, additional cold cathode lights etc.
We'll be calculating the GPU power consumption here, not the total PC power consumption.
Measured power consumption
Advertised TDP = 170W
System in IDLE = 173W
System Wattage with GPU in FULL Stress = 321W
Difference (GPU load) = 148 W
Add average IDLE wattage ~ 25W
Subjective obtained GPU power consumption = ~ 173 Watts
Bear in mind that the system Wattage is measured from the wall socket and is for the entire PC. Below, a chart of measured Wattages per card. Overall this is much higher than reference, this is due to an increased GPU voltage to allow easy overclocking and the standard higher clock frequencies.