Here's another vote for SilverStripe. I've run it in production for a year and a half and been very happy with it's performance and caching options. (You can do partial caching all the way up to a full but automated static export.) The MVC framework borrows a bit from rails and makes it one of the nicest PHP CMSes to develop for. It's much more fun than managing WP custom post types and the interfaces I can create for end users are better. Downsides? Documentation could be better and not as many off-the-shelf modules available. Both LibreOffice.org and OpenStack.org are powered by SilverStripe.