Our performance issues of late (as far as I could trace) were related to our vBulletin search & search indexing not coping with our large volume of posts. I now have us running on a dedicated search & indexing application. This system is highly efficient, used by most if not all vBulletin "big board" owners. It removes vBulletin software from struggling to manage our data search & indexing. It was quite the nightmare to implement but we'll be far better for it. If you encounter search errors or issues please post here.
Search has been replaced, and might be more accurate, faster etc but what you need is more custom. Once the dust settles from the recent issues and updates I'll re-investigate.