Power consumption and efficiency
The workload for this test is encoding a video with x264, based on a command ripped straight from the x264 benchmark you'll see later.
Our Core i7-6700K-based test system draws a little more power under load than the 4790K-based equivalent, which is what we'd expect given these processors' respective TDP ratings of 91W and 88W. Our 6700K system is relatively frugal at idle, too, although it's nothing special there. The Core i7-5775C is in a class of its own on that front.
We can quantify efficiency by looking at the amount of power used, in kilojoules, during the entirety of our test period, when the chips are busy and at idle.
Perhaps our best measure of CPU power efficiency is task energy: the amount of energy used while encoding our video. This measure rewards CPUs for finishing the job sooner, but it doesn't account for power draw at idle.
Even though it draws a little more power at peak, the 6700K-based system requires less energy to encode this video than the 4790K-based one. The difference between the two isn't dramatic, but Intel's architects appear to have succeeded in improving Skylake's power efficiency over Haswell's.