Content does not seem to matter. I have a gazillion notebooks with various contents. Ok movies and audio might cause some performance decrease but otherwise it really should not matter. One thing i always uncheck is the 'Check spelling as you type option'. Furthermore try changing the number of Optimizing files which you can find under File - options - Save and Backup. Also remember that backup takes time if you have many pages. So settings would definitely be a pointer to take a look at.