For what it's worth, I've been using CloudDrive to store my Plex media for the past year and the default settings have always worked well for me.
The reason I posted this question is because I'd like to move all my data out of and away from CloudDrive. After the GDrive corrupt data issue a few weeks ago, I lost a ton of media on one of my drives and no longer trust it being in the cloud, so I'm trying to do a bulk download to physical hard drives.
The default settings do not seem catered to performing bulk downloads, which is why we've been messing with all of the I/O options to figure out what would.
From what I've found so far, the fastest combination of settings seems to be 1MB trigger/20MB forward/30 second time window for the prefetch settings, with 14 download threads and a 20MB minimum download size. I'm fairly certain I maxed out the chunk size when creating the drive, but I really can't remember.
It's still not blazing fast, but it is much faster than the default settings I was using just two days ago.