I have a Proxmox server running two Opteron 6272 CPUs on an Asus KGPE-D16 (chosen because it was the fastest computer that supported Libreboot, although I haven't gotten around to installing it). Using normal BIOS settings, it's drawing just under 100W at idle, measured via smart plug reported in Home Assistant. With aggressive efficiency settings (PowerCap to P-state 4 and disabling CPU 2 entirely) it idles at 70W. It's a server, not a gaming PC, so it doesn't appear to have any options for underclocking or adjusting voltage.

Anybody know of any other ways (maybe software-based) to get the power draw down further?