Thank you very much for your input on this matter.
Thing is that I don't get the long boot every time, it is very sporadic and might not happen for days at end, or then could happen couple times in a row. RealBench and memtest86 don't find anything to be wrong with memory settings.
That is why I am wondering about VCCIO, VCCSA, PLL Termination, PCH Core and CPU Standby. If I leave them on auto, then they get rather high. If I set them low then I still pass stress tests but I suspect that VCCSA introduces intermittent long POSTs. As mentioned, they are so intermittent that there is no way to change the value and go test it out. I would have to do hundreds of restarts to get a result that would have any meaning, so it's not something I can try out by blindly going after five different voltage values. My Vcore is dialed in and stabile, and I am just wondering what I would have to do to get the POST in order as well.
VCCIO: I don't even clearly understand what it does. Sites say that it is used for all I/O pins except memory related pins. Suggestions say to use 1.15. I have no idea what this voltage is used for, what is considered normal and what are the limits.
VCCSA: Memory controller, PCIe and display engine. I think that could be my issue, so should I try increasing it to, say 1.20v? What is the safe limit for this?
PLL Termination: Again, I don't know what it does, what to set it at and what is safe. Currently at 1.0v
PCH Core: Quite simple, it's voltage for PCH. Currently set to 1.0v and thereabouts when it's on auto as well. Don't really think this is my issue.
CPU standby: Again, not clear on function of this one. Set it to 1.0v as auto shoots it up to 1.6v. Should I increase it?
Regarding AVX, I don't use AVX workloads. I am happy to leave it at 0 offset as long as I don't encounter instability. What puzzles me is why does my system start crashing under stress test when I set it to anything from 1-10 and then run loads that don't even utilize AVX. Is the BIOS broken?
I also have one new question. What is CPU PLLs OC voltage. HWiNFO64 reports it at 2.6v and there is no BIOS setting for it. Is that normal?
I will also upload my graphs to third party picture hosting so you could see them in detail if you are interested. HWiNFO shot from current, idle voltages also included. Click for full size image.