Consider installing the Boost module to create static HTML versions of pages that are served anonymously. Cached pages don't even use PHP (they are served as .html files) let alone create or use queries in MySQL so caching is super fast. Cached pages can be cleared on a regular basis with cron. Works with multisites and provides speed improvements to almost any Drupal site. Requires modification of default .htaccess file.
In regards to page compression, you will find on admin/settings/performance a description that looks like By default, Drupal compresses the pages it caches in order to save bandwidth and improve download times. This option should be disabled when using a webserver that performs compression. To find out whether your server already performs compression have a peek at /etc/httpd/conf/httpd.conf (CentOS/Redhat) or /etc/apache2/mods-enabled (Debian/Ubuntu) to find out if the module mod_deflate is called. If so, turn off page compression.
You're done!
