Do you have [RELEASE] Hub Information Driver installed? While it won't tell you what is causing the issue, it does give a good overview of memory and database use.
Another thing I might suggest is to watch your database size. I recently set every device to only store 11 events and 11 states. (Don't use less than 11, it makes the database do constant cleanups, which can slow the hub.) I also set the length to store events to 14 days. I had stuff from a year ago in the database, and I was never going to use that data. Between those two things, it made my hub much snappier. It wasn't slow before, but it was noticeably faster after pruning all that cruft out of there.
And while we are at it, maybe try a backup and restore? Maybe something is corrupted, and that will clean it up.
