My vote is to play it by ear. I believe that the chapter material is what has caused the slow-down in postings, lately. Look at the most recent chapter - The Choices of Master Samwise - the thread is going nuts. I believe that all the way through RotK it will be the same.
So, how about this. Decide about opening a new thread by how many posts are on the last one. If it's more than, say, twenty, pop the next chapter open. If not, let it slide for a week.
To close, let me say that while I haven't posted much on the threads (which I primarily attribute to my not reading the chapters while they are being discussed
), I have thoroughly enjoyed the discussion and taken much away from it.
Whatever the choice, I will continue reading and occasionally posting.