Techpowerup keep delivering all the answers this launch.
They put a 3900X in a cheap ($70) ASUS B350 motherboard. Here are the results:
https://www.techpowerup.com/review/amd-ryzen-9-3900x-tested-on-cheap-b350-motherboard/
Seems to be 2 bad results but otherwise parity, great when you consider this board ranks so low on the VRM tier list:
https://docs.google.com/spreadsheet...MvYeCLI5ZbIpnq5fyiWD4NCkkU/edit#gid=229691480
Awesome info thanks