First time caller, long time listener who's been playing with a 12700k for the last couple months. As a test, I currently 5 1080 streams playing on the Windows VM on Plex and one on the phone, all transcoding down to a small format. I'm measuring only 120-140 watts with few other containers running as well. Transcoding seems to be fine even while editing 4k 10 bit 4:2:2 and 4K 12 bit raw in Premiere on my VM, total usage doesn't seem to break 350 watts at that point and is usually hovering around 240-280 watts.
The only issue I have is with H.265 content, both in Plex and the VM. H.265 without transcoding and playing on devices that handle H.265 well(Nvidia Shield TV) is no issue, but anything else is a fail, even with the latest Plex that just dropped. The same goes for within the virtual machine From my experience with video editing, the 11th gen and newer iGPU is capable of eating 8K H.265 4:2:2 footage for lunch. Unfortunately, I found out the hard way that my RTX 3080 that's passed through will chew H.264 all day long, but it won't even consider touching H.265 4:2:2. I may have to pass the iGPU through someday and use another Nvidia card for Plex.