I'm currently using the Google Compute Engine method as well, thanks for that @Philip_Koninghofer.
Instead of the three parallel screen session I used one screen session with the command:
exec 6>&1;num_procs=10;output="go"; while [ "$output" ]; do output=$(find "$HOME/odrive-agent-mount/Amazon Cloud Drive/Media/" -name "*.cloud*" -print0 | xargs -0 -n 1 -P $num_procs "$HOME/.odrive-agent/bin/odrive.py" sync | tee /dev/fd/6); done
If you get a permission denied error just
chmod a+x ~/.odrive-agent/bin/odrive.py and try again.
This starts 10 threads according to the author of the topic odrive forum's for syncing and gives me higher speed than the other method. I'm averaging around 700Mbit/s right now (checked nload), but sometimes hit peaks of 1.3Gbit. According to a calculator an 8TB transfer will take around 24/30 hours so I hope the data is transfered by the end of the weekend and I can start uploading it to G-Drive again.
Edit: Just to let you know, I tried other methods as well since I thought my odrive expired trail would give issues on linux as well, but it seems there is no issue with syncing the whole drive when using the agent. Also multcloud, cloudhq nor amazon's own client were able to download as fast as Google's compute engine, I guess it's the best bet right now.