Depending on the benchmark, the Core i7-6700K is about 15 percent faster than the i7-4790K, which has the same clockspeeds.
The i7-6700K is a quad-core chip, with HyperThreading enabling 8 logical CPUs. Its nominal clock will be 4.00 GHz, with a rather shallow 4.20 GHz Turbo Boost frequency. It will feature an 8 MB L3 cache, and an integrated memory controller that supports both DDR4 and DDR3 memory types. This makes Skylake a transition point for the mainstream PC market to gradually upgrade to DDR4. You'll have some motherboards with DDR3 memory slots, some with DDR4 slots, and some with both kinds of slots. The resulting large uncore component, and perhaps a bigger integrated GPU, will result in quad-core Skylake parts having TDP rated as high as 95W, higher than current Haswell quad-core parts, with their 88W TDP.