Should be other thread with this info.
Pretty sure 6900xt is same chips as 6800xt just binned for better clocks and lower power.

I run my 6800xt at 1200 core 2150mem fasttiming on. 625mV thru bios mod.
Runs 64mh/s at 136w.
Use to run 64.6mh/s at 137w but for some reason i cant find that sweet spot anymore.
You can get some down to 108w if u mess around with tdp and stuff but I also game so didnt want to push it.