Well, I'm already retired and I can tell you it's not worth moving to the mountains!
I'm not familiar with the Synology router but do use their NAS products so it should be good. The right place to control your internet connection is at the router, having done that you should be able to let IDrive, and any other app, go full speed and the router will sort it out, but it sounds like that's not happening.
Do you have another device you can use to try to max out your connection and see if it dies? Or have another app on the same device as IDrive's on that might be able to max out the connection and see if it dies the same way as using IDrive? We need to work out if it's IDrive, the device it's on, or your router/connection combo...
To me it doesn't sound like a totally IDrive problem - and I would never trust any app to throttle it's data connection as they are notoriously inaccurate and unreliable, hence get the router to do the work.