I discovered this past weekend that if you want to make WordPress grind to a halt all you have to do is import roughly 2000 pages into it. Why did I import 2000 pages into WordPress? Well I wanted to see how it would do. I have a client that has a fairly large Joomla site just over 2000 pages so I did a little scripting and had it import those 2000 plus pages into WordPress.
I did it first as pages, and WordPress failed miserably. The Joomla site has no problem dealing with that many pages in it. If I changed the import script slightly and had the pages import into WordPress as posts WordPress had no problem with that amount of data. Unfortunately the pages should not be called posts, because they contain information that is static for the most part and would only need to be changed occasionally.
The problem WordPress has with that many pages appears to be with how it loads pages. I was using the default Kubrick theme for WordPress and by default it loads all of the pages on the sidebar. Even after I removed the Pages widget from the sidebar WordPress still would grind to a halt on load. In the administration section trying to manage the pages was impossible, because WordPress does not break the listing of pages up into pages, it displays all of them. Not good. The administration panel would simply time out.
If you are thinking of creating a large site with mostly static pages, stay away from trying to use WordPress as a Content Management System and look at Joomla. It will have no problem dealing with that number of pages.