Hello John and Dan
I’ve unwittingly stumbled into this issue too, after upgrading the drives in my Late 2015 iMac. I put in a WD Black drive and it is recognised and works fine, until waking up from sleep when the kernel panic occurs. Can you recommend a 500GB blade that would work with the slower motherboard? Or if I put the WD drive in an external enclosure would that get round the issue, or would the motherboard have the same throttling issue too? A real pain to have to strip the screen off again….