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.
// UK lang variables
tinyMCE.addToLang('',{
paste_text_desc : 'Paste as Plain Text',
paste_text_title : 'Use CTRL+V on your keyboard to paste the text into the window.',
paste_text_linebreaks : 'Keep linebreaks',
paste_word_desc : 'Paste from Word',
paste_word_title : 'Use CTRL+V on your keyboard to paste the text into the window.',
selectall_desc : 'Select All'
});