That's a fun test there. Thanks for sharing!
I tested PBO stuff in BIOS and I can only conclude it's broken/artificially limited on power draw for core power and package power. There are 2 configurations possible on what the board will allow with PBO settings enabled in various combinations.
AS measured in HWiNFO64:
CPU Package Power (SMU): ~110W & ~120W
CPU Core Power (SVI2 TFN): ~60W to ~65W
This limits clocks/voltages the board/PBO will be allow to run and be constrained into. It tries it best with this limit but the limits are so low if struggles to produce results!
Where is that unlimited board power or for that matter design power at 140W anywhere to be seen as advertised for the CPU as said by AMD?
As you figure the higher power draw usually performs better but that depends on settings. In differing combinations one PBO setting will push the core's to use more voltage for any particular frequency, that's bad...
You want the setting that will use less voltage for any frequency. Easiest to see is the combo that doesn't allow the CPU to run 1.500V freely when viewed from HWiNFO64. For me that's around ~1.481V Maximum.
It's a little confusing which combo gives this result at the moment as there are duplicate entries for PBO in various fields in the BIOS and you can set them enabled and disabled at the same time and various ways with Manual settings are in both and divided apart for them, they aren't all in the same place.
In the end basically this means PBO doesn't produce any better Cinebench R20 scores than having it all disabled/auto and sticking with regular PB only!
It uses the lower voltages and your CPU isn't limited to a 110W or 120W CPU Package power limit!
STOCK you get a 140Watt limit without PBO enabled!
With PBO you are either limited for 110 or 120Watts CPU Package Power!
I tested this mostly running Cinebench R20 for now as I wanted to see if I could get better results. It failed to do better than stock scores and then I noticed the limited power draw and well... I hope it's not just Cinebench R20 it does so for.
I had some screenshot from running Prime95 @ stock and it was ~140Watts limited for CPU package Power & ~75Watts CPU Core Power for Maximum values.
I did a quick check with PBO enabled and it used ~113Watts for CPU Package power and ~65Watts CPU Core Power for the first few minutes.
No one else notice anything similar?
EDIT: Ok, I might have been to quick with all this as with further testing Prime95 ramps up on wattage in a later stages up to 140W. Not the first few tests.
But there was still that 10Watt difference for Cinebench R20 between settings I noticed.