I'm running PBO on my 3900X with the latest 1.1.0.0 AGESA--well, been running it for the last 12 months at least (x570 Aorus Master)--and I routinely get 4.65GHz max single-core boost--air-cooled, stock fan, stock clocks, on 3-5 cores (according to HWinfo). From what I've read the main difference between Zen2 PBO and Zen3 PBO is not just a bit higher max-single-thread boost clocks (which are lost if you manually overclock all the cores as boost is disabled) but 5000-series PBOs are also supposed to deliver the higher boost in a more sustained manner--at least "sustained" in comparison with Zen2 PBO boost clocks, that is. Yes, the Zen 2 max boost is there but only in lightly threaded workloads, and very briefly, too.
It's fun to tinker with, but the differences are 200-300MHz, max, over what the CPU will do boosting or overclocked on all cores. Sometimes, people split hairs over a mere 50Mhz difference in max boost clocks. The single-threaded Cinebench tests are, I think, rather silly, as no one is going to render professionally using this program (or anything like it) in single-thread mode...😉 Defeats the entire purpose of multicore SMT CPUs, imo!