I would be speaking about how to increase WordPress performance on the back-end server. Even though most of the slowness of the web is on the front-end, most of the time, there is still some things you can do like caching the database via Memcached (using plugins like W3 Total Cache), running an HTTP caching proxy like Varnish, or using a faster server architecture, like Nginx with PHP-FPM, instead of running Apache.

I could also get into better server configuration settings, like making sure PHP and your web server is ideal to your server specifications. This would be a speech for the people running on their own virtual/dedicated servers, as on shared hosting, they would not have access to these configuration files.