Power up your machine. Put it into lowest power state as you can. Measure it.
Reboot, set in BIOS/UEFI - continue on all errors.
Open the machine, remove GPU completely. Reboot. If it boots till sound, measure - thats raw performance without GPU.
It doesn´t play any role if Xorg was started or no, main point is cpu-governor should start and that happens if kernel and init system work.
You can make a daemon to create some random file at end of the boot as confirmation that machine did boot.
so my 1W less finding may be the zerocore deepest state cause they used an active cooler version there(+1W?) an i have a passive card.
but doas it matter?
0,002kW*24h*365d*0,25cent/kWh=4,38€ /year difference if its idle all the time