Total System Power Consumption
Our goal was to give you an idea as to how much power each configuration used while idling at the Windows desktop and while under a heavy CPU workload. Keep in mind, this is total system power consumption being measured at the outlet and not the the individual power of the CPUs alone.
With two fewer cores enabled and less active cache, it should come as no surprise that the Core i7-3820 consumes less power than its other Sandy Bridge-E based counterpart, the Core i7-3960X. Idle power consumption was similar between the two, but peak power was about 35 watts lower with the Core i7-3820. Versus the similar-performing Core i7-2700K, however, the Core i7-3820 based system uses significantly more power, not only due to the processor's additional resources and larger die, but the additional needs of the X79 platform (quad-channel memory, more PCIe lanes, etc.)
We also wanted to show you what happens to power consumption when overclocking the Core i7-3820. As you can see, with the CPU frequency cranked up to 4.7GHz (and an additional .2v being applied to the CPU), the Core i7-3820 based system pulled almost 100 additional watts from the wall. Having a good power supply is always important, but if you plan to overclock a Sandy Bridge-E based system, having a quality PSU capable of providing plenty of juice is paramount.