The Mac client should, like basically every other client and the daemon, use the settings.json file for configuration. This seems to allow for a more fine grained confugiration, because there are some settings that I can't find anywhere using the Mac version (e.g. upload-slots-per-torrent).
Btw. If there is any way to set "upload-slots-per-torrent" using version 1.91 on the Mac, please let me know.
Edit: Nevermind, I've created a patch that adds upload-slots-per-torrent to the Mac client. However, it would be nice if settings.json and the plist could be more in sync.