CMS that servers static content that isn't rotating lots? You should possibly look at runnign a reverse proxy cache then. I've had fantastic success with Varni

CMS that servers static content that isn't rotating lots? You should possibly look at runnign a reverse proxy cache then. I've had fantastic success with Varnish. I've been able to increase the performance of Drupal by a factor of several thousand by running Varnish. Since you are running a CDN already then I assume you have moved all of your static assets off onto there.