Ok granted we have seen these leaks many times already. A screenshot of CPU-Z shows a clock-frequency of 5.2 GHz on a Core i7-6700K, that would be Skylake. According to Chinese based Hkepc they achieved this clock frequency on air cooling. It isn't stated if the CPU was stable or not.

The 5.2 GHz would be reached at 1.35V in combo with a system that runs, get this, Windows XP. In a teaser video Hkepc shows that the processor runs at 5 GHz stable at 1.286V, a screenshot proofs that SuperPi was running. 5Ghz at 1.286V is not bad, not bad at all. BTW the value in the CPU-Z screenshot is a notch lower, often releated to a bad software readout.

The Core i7-6700K is an engineering sample from intel, the chip runs 4 GHz at default base clock with a Turbo towards 4.2 GHz. The quad-core processor has 8MB cache and a 95 Watt TDP. Rumors suggest that early august this product series will launch. 

Thanks to Daniël de Jong for this spot.

Skylake Core i7-6700K clocks to 5.2GHz on air cooling