Thanks for your help @Ole!
Decided to laeave things alone well past the 1.26 days. Started running this command rclone --ignore-existing --checkers=16 copy -P with no other flags as you suggested and it's going great now 
Many mixed file sizes but the current rate is showing ~33 Mbyte/s with no warnings as yet.
Will add the cloud-specific backend config entries added afterwards, really appreciate the info!