Silicon Lottery put up a small batch of 9700Ks last night, but the 9900K date got pushed back (again) to November 9th.
Predictably, all but the middle bin is already sold out.
Binning stats for i7-9700K:
As of 10/28/18, the top 28% of tested 9700Ks were able to hit 5.1GHz or greater.
As of 10/28/18, the top 69% of tested 9700Ks were able to hit 5.0GHz or greater.
As of 10/28/18, 100% of tested 9700Ks were able to hit 4.9GHz or greater.
They were thermally limited by 240mm-360mm AIO coolers and say you can get a little bit more Hz by increasing voltage to 1.4V+. But at that point you're looking at as much as 200W+ heat dissipation, so you need a custom loop to keep up beyond 5GHz.
That's for the 8c/8t chip. AIO is obviously not going to be enough for a stable 5GHz+ on the 9900K unless you have extreme airflow and a golden chip. Or set a big enough AVX offset.
Edit: Clarified point about 8th gen Core scaling with voltage (as long as you can cool it).