At the risk of being reprimanded for cross-posting, I want to share the solution to the page-loading performance issue in 2.3.1 that was bugging us this past month.
Via the Moodle Tracker I got a tip that really made a big difference in our site. We had already upgraded to the latest release of 2.3.x which resulted in some performance improvement, but a simple setting seems to have been responsible for a large part of the slow page loading in our case:
See if you have Open in new window turned on in Site Administration > Appearance > Moodle docs. We had it turned on (seemed harmless) and reverting to the default No resulted in a substantial improvement in page loading times.
Others also report that turning off Show all courses in Site Administration > Appearance > Navigation has a discernible effect on performance.
Page loading is still slow in Internet Explorer, though, but it is better than it getting totally stuck. However, I am confident that over time further performance improvements will be achieved in Moodle 2.3.