I've been working quietly away, mainly posting on Slack. I have used and tested both rclone / acdcli with UnionFS and OverlayFS. I've come to the conclusion that rclone mount + crypt with local storage and ACD using OverlayFS to be the best performing setup. I've created a custom complied kernel v3.18.48 and v4.4.52 from source to modify the FUSE parameters in use by rclone mount to further increase performance.
Server I'm using is a online.net dedibox lt 2016 running ESXi with Debian 8, custom 4.4.52_1 kernel (600GB local SSD, 24GB RAM, 8 CPUs).
My location UK.
Software: Plex v1.34 (v1.4 is worse performing)
Rclone Latest Beta
You can find my scripts and kernel on my GitHub along with install of all of it. https://github.com/jaketame/plexacd/
Download locally and retain until disk is 80% full then upload, pausing NZBGet while uploading and also only uploading during the hours of 01:00 to 15:00. NZBget is paused for downloads during 15:00 to 01:00 to ensure smoother playback.
I use OverlayFS to merge ACD and local storage.
Plex will load from 2-5 seconds with no buffering or stuttering. I've disabled all scanning from Plex. Sonarr/Radarr update Plex on download.