While I'll fully agree that expecting any i7-6700k to hit 5.2 GHz would be overly optimistic... SKL overclocking being markedly better than anything since SNB wouldn't be surprising in the least. For one thing, recall that SKL is a Tock from Intel's Haifa design team just like SNB, whereas HSW was done by their Oregon design team. That's not saying that one team is better or worse than the other on the whole, rather a mere suspicion that the Haifa team may well design in more margin on the timings which would result in better overclocking capability.
Cool info. I've always been a sucker for this stuff. I used to really follow which team was on which core, I assume the Haifa team is the Israel one? I remember the Oregon team being in charge of the big stuff like Nehalem and then the Israel team always followed suit with more efficient stuff.
I personally always thought that it mattered what team was working on the chip, and that one was possibly not better overall, but better in certain areas than the other one and vice versa.
Like when the Israel design team dropped banias (Pentium-M), it basically set the precedent for the future Intel design goals. It was the 1st generation of the Centrino laptop ecosystem the seed for Conroe, and more efficient chips then netburst in general.
Those were the good ol'days~ Here's hoping skylake brings some innovation~