How about a P3/P4/P5 flag for the threads and, as shadowcat suggested, only showing the first (and maybe the last) posts in the thread when rummaging through the forum? That way, you would be able to distinguish P3/4/5 content and you would be able to see a larger list of the messages rather than 25/page when there is multi-hundred posts. The flaging should take less coding/admin time than seperate fora. The post lists seem like it would be an easier task as well with only first/last posts showing. Or, perhaps, another setting could be placed in the "Edit Forum Preferences" that would allow you to specify showing only P3/4/5/all posts and/or how many posts/page you would like to see?