Chiiiiiiiiill out.
First of all the market needs some to react to this with price changes.
About the 6600K and 6700K: I really don't see the point yet.
Still more a lot more expensive than the 4790K, no cooler, only Z170 mobos available for now, both make the whole ordeal even more expensive and the IPC increase isn't enough to make up for the clockrate.
Overclocking statistics are sparse, so there's not much I can say yet.
1. Thermal paste again, so same problem as Haswell.
2. If you don't have the cooling power to go to 1.4-1.45V (and you'll need a beefy cooler, see 1) you're looking at 4.4-4.6GHz on the 6700K, lower on the 6600K.
3. Even with >1.4V only 4.7GHz are possible consistently, only a few samples are stable at 4.8GHz, almost one above that.
4. Delidding will be very interesting.
I'm not surprised at all and I didn't expect the K SKUs to be worth it. The 6700K might be interesting if you're overclocking just for the hell of it and delidding.
BCLK overclocking on the non-K versions, maybe on non-Z170 mobos will be interesting. Since Skylake is mostly thermally limited if all the CPUs are using the same thermal paste all those that aren't as close to the max TDP that it can handle should see some easy (and in case of non-Z OC even free) gains. With the clockrates almost unchanged from Haswell this could lead to a significantly better price to performance ratio, even with higher prices and more expensive new motherboards.
Not sure what the 5820K has to do with this. It's a more expensive 6 core on a more expensive platform. On anything using 6 cores it beat the 4790K and it still beats the 6700K, not surprising with 50% more cores. Using 4 cores or less the 4790K beat it and the 6700K beats it aswell.
FYI the 5960X still has 8 cores and is still cheaper than an equivalent Xeon. Quadcores don't compete with Hexa- and Octacores. Not within 2 generations. A platform with 16 PCIe lanes doesn't compete with a platform with 40 PCIe lanes. Intel doesn't compete with itself.
Also what kind of recommendations are you reading that you think the 5820K is an option for you?