Thank you for your interest.
No doubt SdFat is more efficient than FatFs and my wrapper, not only on memory usage but also on velocity.
I have a FTP server running on Arduino Due using your SdFat library with short names.
I modify this server to use FatFs, so I can store/retrieve files and directories with long names. But the byte rate has been reduced by about two. I guess it comes from the way in which the SD library access the card reader, less efficient than SdFat.
So it will be interesting to be able to use SdFat again for this project.