@lopri no dice, 102 MHZ bclk was not stable. My machine just doesn't want to "go there". I had the same problem with my 1800x despite choosing a board with an external bclk clockgen chip. I think I would have had to use a SATA SSD connected to the chipset ports (7 or 8) to make that work. My BPX, which was in that old machine and is my backup NVMe drive in this box, is allegedly sensitive to bclk as well.
However, I did discover a few other interesting tidbits.
First off, my board has VRM current settings. Overcurrent to the VRM (increase their switching frequency, basically) along with LLC appears to stabilize the CPU at "bleeding edge" voltage settings.
In CBR20, with Medium LLC (which is LLC2, I think; Low =1, Medium = 2, High = 3, Turbo = 4, Extreme = 5, Ultra Extreme = 6 hahah thanks Gigabyte) I needed 1.31875v vCore to get stability @ 4375 MHz all-core. Actual vcore according to CPU-z was around 1.332.
With Turbo LLC and "Xtreme" VRM current setting, I can use Turbo LLC and 1.29375v vCore to get stability @ 4400 MHz all-core. Actual vcore in CPU-z is a1.32v. VRM temps go up when you crank up VRM overcurrent, which is a problem for anyone that has hot VRMs. During a CBR20 run with "Xtreme" VRM overcurrent, my reported VRM temps around 38-39C. No problem for this board.
Then I did some research into the effects of LLC settings on default and PBO behavior. I ran the system in bone stock config, with only "Xtreme" VRM overcurrent (no reason to avoid it) and different LLC settings to see what would happen in three benchmarks: CBR20, SuperPi 1.5mod XS, and 3DMark CloudGate Physics. I tested Low, Turbo, and Ultra Xtreme.
Code:
LLC Low
CBR20 default: 6961 PBO:6961
SuperPi 1M default: 9.796s PBO:10.008s
CloudGate Physics default: 12630 PBO: 12861
LLC Turbo
CBR20 default: 6853 PBO: 7013
SuperPi 1M default: 9.561s PBO: 9.255s
CloudGate Physics default: 13461 PBO: 13213
LLC Ultra Xtreme
CBR20 default: 6792 PBO: 6944
SuperPi 1M default: 9.763s PBO: 9.828s
CloudGate Physics default: 13483 PBO: 12800
Seems like there wasn't a lot of consistency here.