get a platinum rated power supply, if you can afford it go for a titanium. The efficiency in the power supply is half of the efficiency of the rig
reduce the number of the modules to the minimum
get a platinum rated power supply ;)
get big passive coolers, you want to idle the fans
reduce the number of usb and connectors to the minimum. Their converters are not the most efficient. Try not to connect enything on them.
NO mechanical parts (including fans or water coolers)
set schedulers to conservative or power efficient. You don’t want to spike the power just because a task is 2ms longer than expected.
pick a power efficient CPU/gpu (I think we can discard this one based in your choices)
use the latest amd adaptative undervoltage technology to ensure to reduce the wattage of the cores
try to reduce to the bareminimum the number of background tasks /services running.
And that’s all. Sometimes there is a component of trial and error because sometimes the curve performance / power is not entirely linear and you don’t want to hit exponential-non-linear zone.
Good luck and if you can post you build with numbers and some lessons learnt would be great