What are you on about.
The £650 binned 8700K at 5.1 which I'm taking your word for exists, does it on all cores at once.
5.1 on an 8086K is from it cutting the clock on 5/6 cores and pushing the best core to 5.1.
This is not special for this CPU or for Intel, it's a thing for every high end CPU these days, the fanciest boost clock is what it can get by sacrificing the clock speed of all but one core.
You could have taken 10 seconds to click on the overclockers link rather than take my word for it but i'll make it easy for you: https://www.overclockers.co.uk/inte...e-socket-lga1151-processor-oem-cp-00m-oe.html
With the 8086K it will likely be a case of enabling MCE and an easy 5.1 on all cores, so I stand by it making the binned chip pointless (unless you want to pay that much for a de-lid)