was hypervisor overhead significant in your case?
from observation basically ~1%
no hard numbers
likewise (pure guessing) you draw more power if you have the vm with gpu path trough enabled because the gpu is not gonne go into sleep any more - no idea if 0,1W or 10W
overall remember proxmox/debian/linux does not enable all power saving options by default, you need to manually enable them to save some additional amount