So here are some actual time runs for you…
Copying a 1GB file
13 secs. From Cloud to my Mac (flash drive) = 78MB/s
13 secs. From Cloud to my PC (flash drive) = 78MB/s
15 secs. From PC to Cloud (write) = 68 MB/s
13 secs. From Mac to Cloud (write) 78MB/s
29 secs. From Mac to Cloud USB WD 4TB = 35MB/s
30 secs. From PC to Cloud USB WD 4TB = 34MB/s
Copy (meaning read then write)
21 secs From Cloud to USB WD 4TB
38 secs From Mac from Cloud to USB
34 secs from PC from Cloud to USB
You could probably find a FTP program that allows you to log into the Cloud and probably the shared USB at the same time and simply drag and drop the files using the Cloud to handle the transfer, although I don’t know how much Cloud CPU for the FTP that this might entail, you may have to find an FTP program to test it out, but I would find it extremely annoying to use since it is not in our normal windows friendly environment of simply mapping the drives and drag and drop.
I use a program called “beyond compare” that has versions for both PC and Mac. This program compares the files between the Cloud and the USB and tells you which files has changed since the last sync. You can then simply copy the ones that have changed.
I prefer the use of this program for the reason that it doesn’t accidentally sync changes on files that have been deleted in error; it is all user controlled. Although it takes longer of having the PC in between to read the data over to the PC before writing it back out to the USB, I have the advantage of seeing which files that I need to sync in a drag and drop format.