Thanks for the save game,
I managed to find a really good optimization using your save game. There was an internal flag to force paths to complete when work is started, instead of spreading it over over several ticks. Enabling that flag for the drones resulting in the client queue dropping to 0, and pathfinder workload dropping significantly:
I can now play your save game at nearly 100UPS, compared to 55 or so UPS before.
Another advantage, is that the drones no longer just hang around when deploying, they get a path very quickly and get to work.