I don't usually push this machine too hard - maybe the most that I do is recompiling ffmpeg a few times a day, so it might just be a result of my usage patterns? I'll get back to you with more solid figures later tonight.
EDIT: Just had a play around with sysbench running a few prime number tests while compiling a kernel or two. The k10temp-pci-00c3 (CPU temperature under lm_sensors) seems to stick around at a crispy +64.1°C for a good few minutes, before rising to +65.6°C. It seems to drop back down to +64.2°C. The fan is pretty noisy. The CPU drops down to +50.0°C within 60 seconds of the sysbench benchmark stopping, and the fan noise is completely gone after 90 seconds. Temp is +36.9°C. Idle temp looks like it's around +34.4°C. Not sure how I can measure the db level of the fans? I do have a recorder, so I might be able to do it that way.
Not sure what a good way to actually benchmark the machine would be - it hasn't really come up as a necessity. Maybe I can use the Phoronix Test Suite?
EDIT 2: Doing some searching, maybe I got the machine just in time? 5.17 looks like it added some code specifically around P-states for Linux. https://kernelnewbies.org/Linux_5.17#New_P-State_driver_for_... ... Someone else with my exact same kernel version reports AMD issues being fixed in Arch that they previously had. https://www.reddit.com/r/archlinux/comments/u7kwza/recent_ar...