Following up from my previous post here, I moved over the stuff to NR200, used a new thermal paste (MX-5), and ran Cinebench r23 for a while, it now runs much cooler, 75c max at 4.4 GHz @ 1.175v vs 85c at 4.3 GHz at same voltage with MX-4 paste, that's quite a drop in temp (both still with same cooler, Noctua NH-D9L).
With temps less of a concern now, I'll give PBO/auto OC another go and see if I can get it working properly this time, but if I can't get that sorted out, I can push the CPU some more with manual overclocking instead.
Edit: got PBO working nicely, my issue was setting voltage a bit too low, left it on auto and it's working wonderfully, up to 4.8 GHz single core, 4.6 GHz all cores (actually doing these clocks, the effective clocks are showing these numbers, so I got rid of the clock stretching issue, yay), max 80c, I have PPT set at 105w, +100 MHz offset, I could increase the PPT by another 10w and see how it goes.