I made an script to run devcon, overdriventool and finally cast xmr. I set the Task Scheduler to run this script at statup whether user is logged or not. When booting the pc and not login the script will run in background, without opening the cmd prompt.
This result in a consumption of around 1015W in a 6x Vega 64 rig.
If I run the script manually, so it shows the cmd prompt, the power consumption is  between 100 and 150W higher.
I don't understand why this happen. I would like to know if you can replicate this results.
Of course, the downside of this is that you cannot know the hashrate you are getting.

Devcon wasn't running properly.