I solved this for me like this.
I downloaded “Rivatuner Statistics Server” added Gems of war and limited it to 60 fps
Then I updated the file “GemsOfWar.exe.cfg” under “C:\Program Files (x86)\RivaTuner Statistics Server\Profiles”
with “IdleLimitTime=1000000” under “[Framerate]” like this:
[Framerate]
Limit=60
IdleLimitTime=1000000
This limits the background fps to 1. 100000 would be 10.
Background CPU is now ~4% and GPU <1%
PS: I use power saving mode from Gems of war now but I am not sure how this works with my Nvidia settings maybe you have to play around with it.
I use HWiNFO to check power consumption in watt for CPU and GPU