The answer to this is so complex and depends on so many factors, that it is very difficult to answer. It depends on the feed and the temperature, as well as the pH Value. Also the consistency of your feed. To get a much better answer that what I can provide, do the following:
Take one of your worm farms, remove the lid and put in under a light. Add 2000 extra worms and wait 3 days (with the light on!). After 3 days, switch the light of and wait 30 min. Go back to the worm farm after 30 Minutes and check if worms have escaped. (Don't forget to check!) If no worms - or very little worms - escape, repeat the process until they do, making sure that you keep the light on for 3 days before you test the "runaway rate"
When a lot of worms run away, remove 1000 and theres your maximun capacity for your box, using your food and with the temperatures that you have.
Sounds tedious but its the most reliable way of getting a result...