Umm, as for cooling, I can speak a bit for various cooling for the 6700K and overclocking with my experience. As I've gone through a few with a big order to build myself a system and systems for a few friends all at once. Basically the 6700K will always reach 4.4Ghz regardless of the cooling solution used in my experience. Getting over 4.4Ghz is the rub though. Better board helps a little, better cooling helps a little, but even with the best board and really good cooling, you might get 100Mhz more on a 6700K if that is the absolute max of that chip. The 6700K really is luck of the draw on overclocks. Some can reach 4.9Ghz with shit cooling on shit boards. Others won't go over 4.4Ghz with the best setup. Even turning off HT does nothing for the overclocking potential of 6700Ks. It's a massive pain in the ass lottery. I hadn't tried the 6600K series, but from what I read/heard it is similar for overclocks.
So when people say the average overclock for a 6600K is 4.5Ghz and the average for a 6700K is 4.4Ghz that is pretty damn spot on. Going over those is basically winning the lottery. My current rig was the best of the lot of 6700Ks I tried. Of which I tried about 5 of them. It hits 4.7Ghz, but ran hotter and with higher voltage than I would like even if it was stable with at least 24 hour prime95 stability and a few other burn/stability tests. But at 4.6Ghz it does so at much lower voltage and lower temps for stability. So I leave it there. Of the other chips only 1 could do 4.6Ghz stable but it was hot and high volts. 2 others hit 4.5Ghz no problem but weren't stable at all over that. The last one ran beautifully at 4.4Ghz, but wouldn't go a lick over it. Wouldn't even post regardless of what I tried with it. I could under volt it at 4.4Ghz and it ran cool, quiet, and stable, but anything over 4.4Ghz was a complete no go.Very strange chips these 6700Ks. Anyone that has good low voltage/temp 6700K chips over 4.6Ghz are very lucky bastards.
Still, over all I can't tell a real performance difference between 4.4Ghz and 4.7Ghz with a 6700K when I was doing all my testing. So while I kept the "best" of the bunch for personal bragging reasons, I didn't feel like I was giving my friends shit because their cpus didn't reach 4.6Ghz or higher. In fact I left them all at 4.4Ghz on purpose because it was just nicer for them really as the temps and volts were better that way. Most of them opted for cheaper air cooling solutions anyhow and for the most part their systems were quieter than my water setup with that fans on my rad.