The LGA2011 platform and Sandy Bridge-E processors have never been particularly economical. At full computing load the power consumption of configurations with six-core CPUs like the Core i7-3970X would be twice that of LGA1155 or LGA1150 platforms. The Ivy Bridge-E CPUs may change this situation, though. First of all, instead of 32nm technology they are manufactured on 22nm technology with 3D transistors. And secondly, the Ivy Bridge-E semiconductor die is simpler because it has no disabled CPU cores.
We can also expect improvements in this respect because the TDP of the senior model Core i7-4960X Extreme Edition is reduced to 130 watts whereas its predecessor had a specified TDP of 150 watts. It may seem a minor difference (and the junior Ivy Bridge-E models have the same TDP as their Sandy Bridge-E counterparts) but Intel is known to specify its TDPs with a large safety margin, so we can only see the full picture in real-life tests.
So now we are going to measure the power consumption of the entire Core i7 series for the LGA2011 platform. The graphs below (unless specified otherwise) show the full power draw of the computer (without the monitor) from the wall socket. It is the total power consumption of all system components. The PSU's efficiency is taken into account but our Corsair AX760i is a highly efficient 80 PLUS Platinum product, so its effect on the result is very small.
The CPUs are loaded by running the 64-bit version of LinX 0.6.4 utility with support for AVX and FMA instructions. Moreover, we enable Turbo mode and all power-saving technologies to correctly measure the computer's power draw in idle mode: C1E, C6, Enhanced Intel SpeedStep and AMD Cool’n’Quiet.
The LGA2011 platform still consumes quite a lot of power in idle mode in comparison with the other platforms. The Ivy Bridge-E CPUs ensure certain benefits over their predecessors but the overall picture remains the same. Clearly, the problem is in the platform design which implies that the CPU has a complex uncore subunit without a flexible power management mechanism.
It’s somewhat different under single-threaded loads. The Ivy Bridge-E CPUs turn out to be more economical than the Sandy Bridge-E models or the AMD FX-9370. On the other hand, the LGA1150 and LGA1155 CPUs need even less power.
The new Ivy Bridge-E CPUs aren’t very economical at full loads, yet they are better than their Sandy Bridge-E counterparts. The Core i7-4960X needs 85 watts less than the Core i7-3970 whereas the Core i7-4930K needs 68 watts less than the Core i7-3930K. Thus, the new 22nm six-core CPUs from Intel offer higher performance per watt than their predecessors, largely due to the fact that the Ivy Bridge-E CPUs work at lower voltage.
By the way, the quad-core LGA2011 processor Core i7-4820K is close to the Haswell-based Core i7-4770K in terms of power consumption. This is rather an illustration of the increased power requirements of the LGA1150 platform than of any improvements in the Ivy Bridge-E design. After all, the new Ivy Bridge-E CPUs, even though reduce the power consumption of the LGA2011 platform, do not make it economical. You should avoid this platform if you want an energy-efficient computer.