Okay, just updated to the F42c BIOS that has 1.0.0.3ABBA. Running the same PBO off, -0.075V as on F42a, and idle seems slightly more stable. CPU-Z is not benching single-core properly because the loaded core only runs the bench at x42.8 while said core can clearly hit x44 (the fastest core went from x43.5 to x44, and three other cores are now hitting x43.8 max).
One problem though, Ryzen Master and HWInfo are reporting different temperatures. This is really annoying. I trust Ryzen Master due to its update interval but HWInfo gives me a better idea of max/min and shows me whether WHEA errors are popping up. And this is on the new 6.12 release of HWInfo too. And the histogram issue on Ryzen Master remains, where if you want to use the histogram, Ryzen Master will keep one core at 4.2GHz at all times so your idle temps can't be lower than 45c. And it'll stay that way until you turn off histogram.