"i would still point to the mobo as the culprit - but only you can test that anyway"
I think that @BradB111 most recent data indicates that the motherboard is likely not the culprit. When the load is shifted to CCD1, the motherboard is actually doing everything identically. The CCD1 core is actually not that much worse than the CCD0 as you had indicated. The frequency is within 100 MHz, and the voltage and amperage are only slightly higher. So yes, it is less efficient, but not substantially.
But what is substantial is the temp difference. A 10C delta just by moving to a different CCD is considerable. And I really doubt the block is responsible for that.
Although likely true (Although I really hope not) it doesn't necessarily explain the strange behaviour when I use a voltage offset. and I do think the added temps could quite possibly be due to win background processes sitting on other cores on CCD0. Awaiting your results (I ran mine with all my usual programs open, Discord, Whatsapp desktop, steam, etc....)
May retest with minimal possible programs running.
"I just hope its a case of background processes elevating CCD0 temps"
Hmmm, that is possible, but should also be fairly easy to test. Under process lasso, you could limit all applications on your PC to the CCD1 cores. Then assign Cinebench only to your best core on CCD0 and run the single threaded test. Any improvement there?
Well, good news and bad news. I ran the test on my PC, and I actually see the same thing you saw, which is not what I was expecting. Running a load on CCD1 had lower temps by about 10C vs the same load on CCD0. However, my absolute temps are about 15C lower than what you are seeing. Good news, the CPU behavior actually appears normal. Bad news is we are right back to the original issue.
It will be interesting to see your temp vs frequencies by letting Open Hardware Monitor run for a couple of hours when using your computer.
That way we can see better if your temp are lower with same frequencies or not. I also notice an average difference of 15°C between CCD1 and CCD2, but stock, the frequencies are higher on CCD1 as you can see in attached capture.
BTW, forgot to mention that, so far, no more crash since setting my PSU to 'typical' power instead of AUTO.
And also, that I noticed my average temp went down by a couple of degrees since applying last Asus Bios 3501.
Might be to early to be sure that the crash issue is solved but that is definitely more stable...
I think as far as @BradB111's issue was concerned, I was hoping that we had narrowed it down to the CPU. But, as you say, it appears to be typical behavior for CCD0 to run 10C hotter than CCD1 with the same amperage/voltage applied. However, @BradB111 is still running about 15C hotter than I am on his Ryzen 9 5950X. We have similar EK cooling setups. One caveat there is that my RTX 3090 is not currently in the loop. So I will look at temps again once it is.
We seem to have identical Windows and PBO settings at this point. The only other differences are he is using an ASUS X570 Impact motherboard, and I am on an ASUS X470 Crosshair VII. There was some weirdness with the Impact motherboard, in that @BradB111 noticed the CCDs behaved different when he had a voltage offset in place. And also ASUS programmed bizarre motherboard PPT/TDC/EDC limits for the Impact, where EDC was actually lower than TDC.
There is a thread with an almost identical setup.
From what I can tell, the only major difference is the CPU block and the RAM used.
Okay. RTX 3090 FE has been added in to the loop. All temps are about 10C higher.
So I am now running about 70C in single core and 78C in Multi. Clock speeds have dropped a bit as well. So while they aren't quite as high as yours, we are probably within margin of error now. That RTX 3090 really adds some heat.