So for fellow AMD GPU users using #Linux / #LinuxDesktop (especially for #LinuxGaming ) I just found out something interesting. amdgpu exposes a /sys/class/drm/card*X/device/hwmon/hwmonX*/power1_cap which, as you can guess, sets the maximum amount of power the GPU can use before it starts throttling. There are also power1_cap_min and power1_cap_max values. My power1_cap was showing up as 0 which I guess means let the card's firmware do whatever it wants. (There is also a power1_default value which was set to the same as the max on my system, but apparently default does not mean default here. 🙄 )

I've set power1_cap to the same number as power1_min and indeed, on those things that push my system to the absolute max, I see less overall power usage and lower GPU temperatures.