Just out of curiosity, were you able to find any documentation about the limitations for these machines based on their power supplies or is your knowledge just from trial and error?Can't speak for the older m910x but on mine, the CPU power limits change according to the power supply you plug into it. 90W will dramatically limit a 65W Coffee Lake CPU and to some extent the i7/i9 35W too. I am running a 50W GPU alongside a 125W CPU on my P340 and have no problems... but that's with a 230W power brick.
Thanks!