I'm running all of my forums on php5/mysql5 with no problems.

PErsistant connections maintain a static connection to mysql, which can cause load problems.

Other things to check are that the post tracking options are disabled (Show total # of unread posts per forum?, Show total # of unread replies in topics?) as they can and will cause load on a busy forum.

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
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