I tried using syncthing as I liked the idea of not relying on a cloud provider, but it seemed to be really slow. So slow that I gave up and setup Google Drive. (even over a local network syncing a 2gb file was going to take hours even though I could download that file from the internet in a couple of minutes - is special configuration required to make it use the local network?)
There shouldn't be, somethings going wrong for you. I use syncthing to sync gigabytes of music from my computer to my phone and it takes a couple of minutes over wifi. Syncthing will automatically exchange all known addresses that your device can be found at between your paired devices, and it will then normally use the local network. Not sure whats going wrong for you :/
The Syncthing developers themselves are using Syncthing to sync dozens of megabytes of data. I saw in one of their forum comments.
I tried to setup a drive with roughly 2TB of data. It was extremely slow to get synchronized between my mac and linux. Both in same LAN. Syncthing seems to be a lot of checksums.
I have all the computers connected via (my own) VPN servers, and the only limit for me was my connection speed (which on cable was 1gbit, on some random wifi, slower).
The nodes are set by default to have local discovery, but you need port 22000(?) open for synchronization to work (if you have firewall enabled)
