It would seem logical that it would provide a slight performance advantage to use a DB (Mysql or Postgres, both are supported) but it is going to be a very minimal gain in my opinion. Settings are only read in from a file/db when you login, so normal page loads are not going to be affected by settings storage. Contacts are read from a file/db more often, but even then it is mostly limited to the compose and contacts pages.

Overall the biggest performance related issue on the server-side is your IMAP server speed and extension support (for example IMAP servers supporting the SORT extension have a very nice performance advantage).

If you decide to try db support please note that the mysql contacts table sql has been updated in SVN since the last release to increase the size of a field that otherwise causes problems when you have too many contacts. You can always grab a tarball of the latest SVN from the link at the bottom of our Download page.

Thanks for the feedback,
Jason