As I remember, you look at splitting at about 175 publishers.
Actually, the last few years I was around them, they would try and force a split at 120 or so. Leaving 60 per new hall. Of course, out of those 60 maybe 45-50 would attend on Sundays. One congos we went to had just built a new KH, it had seating for 200+ in it. Of course, right after building it, they forced a split, and we often had anywhere from 65-90 people attend most meetings. Nothing more depressing than sitting in a huge hall that's 30-45% full. Of course, the funny thing is everyone would sit in the back, leaving the front 10-15 rows empty. Bad when you're on stage and can barely make out that there are people in the audience