After many weeks of fighting my system hard freezing, lock up, with no relevant BSOD (if i ever got one) I was about ready to send the board back. (Extreme4 Z270)

After trying everything under the sun to cure my OC freezing problems I finally bumped the PLL to 1.15V and have had a stable 5ghz 7700k overclock since. @ 1.4V LLC - 2 (1.395 in bios) I was able to lower the PLL to 1.14V after finding minor infrequent instability from 1.13V

PLL will increase your temps but i'm running 2x240mm copper rads, one in the front of the case push/pull and one at the top of the case in push config. Arctic F12 Fans, I can crack mid 70's briefly when running stress tests. Idle is 30* on the hottest core and mid 20's on the rest. Gaming I see in the 50-low 60s (GPU is in the same loop 1070)

Just posting this in hopes that it helps someone else out  that encounters this issue in the future.

(Some tags to help people searching this issue, like I did for so long)
ASRock Extreme 4

7700k

Hard Freeze
Lockup
Lock-up

Hard Freezing