Well I'm an idiot - the fulltext index on page_text was missing from a default installation. It didn't break searches but probably slowed them down tremendously. Also set engine to MyISAM on page_text to avoid cryptic error messages from MySQL.

// EN lang variables

tinyMCE.addToLang('',{
autosave_unload_msg : 'The changes you made will be lost if you navigate away from this page.'
});