Thought I'd share my recent project with all of you to see if you can all benefit from it. It is a standalone script responsible for monitoring active Plex streams and throttling your NZBGet client according to speed intervals you define.
https://github.com/daghaian/nzbthrottle
Please let me know if you all have suggestions for improvements as I'm sure there are still some kinks that need to be worked out. Enjoy!