Is there anything that triggers a bell in your mind which might directly affect performance, in the Admin settings? A few things you can ask me to check?
Off the top of my head I can't remember all the things I modified. But going back through some of the Options pages. I think I increased "Store drafts for X hours:" to 24 hours (I don't remember the default). I enabled proxy images because without that, our HTTPS/SSL breaks. (disabling this didnt seem to speed it up)
Kind of at a loss. It could be anything.