Cool, that seems to have helped. FPS/UPS hovering around 36 in empty areas, FPS around 20 (UPS still 36) when in areas with lots of belts and entities on belts.

I'll increase the speed by 0.1 until it breaks, 0.6 is pretty slow

Started with a 29 MB save file that I got from a friend. The train system was broken, so only 3/20 were working. Loaded the save file on a Ubuntu 17.04 VM, hosted it on a headless server, and was able to get multiple people to connect.

After fixing the trains (which consequently kicked off ...