[amcd]

8000 was just an example. We have a thread with more than 700,000 posts. The admins did not like members doing off-topic chatting in any and all threads, so the members made a thread only for chit-chat. Now that thread takes 20 seconds or more to load, and we have quite a powerful dbserver. We keep that thread closed, and another 'current' thread is present for chatting. The current thread is merged with the main thread once it reaches 8000 posts or so. The members are not happy with this.

I read elsewhere that large forums auto-split threads larger than 1000 posts. We have hundreds (maybe thousands) of threads significantly larger than 1000 posts.