I promised to take make another thread for bitrate predictability discussions. Instead, I found this.
https://forums.plex.tv/t/how-to-pre-encode-to-avoid-transcoding-using-vidcoder-presets/
@PlexyChip touches on almost all of the points here, and has excellent references and links to other relevant discussions. He’s done more homework than I was planning to do. I added some screenshots there.