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
System in IDLE = 163W
System Wattage with GPU in FULL Stress = 355W
Difference (GPU load) = 192W
Add average IDLE wattage ~3W
Subjective obtained GPU power consumption = ~ 195 Watts
Mind you that the system wattage is measured at the wall socket.