I get input lag in Windows around 100-150 dwarves. It feels like the GUI not registering clicks, but since the GUI is a separate thread on top of DF it's possible that events are simply lost if a step of the simulation takes a long time. E.g. the selection box will keep running underneath the autosave window or complex world events (migrants, beasts, caravans, season changes), and I think I'd rather have that then random buffered events all playing at once, but certainly GUI integration could be improved a bit.