In the long run, with a board that keeps growing and growing, the posts should be split up as sooner or later you end up with a huge 1.5 GB table that still continues to expand and is less effective to deal with.
Splitting up and arranging them according to time/date (ubbt_POSTS_2008 , ubbt_POSTS_2009 , etc.) seems to be the most logical way of doing it, especially when it comes to the search function.