Slow page loads - unable to determine the cause
If a 304 is taking 5+ seconds that means you webserver (most likely Apache) is being very slow. The ONLY other thing that could be causing this is if you have Far-Future enabled with the CDN module (and that's a stretch). Aggregating should help, as this will reduce the # of requests hitting Apache. 

What web server are you using? Also noticed that Clean-URLs is disabled so I would bet that the webserver needs to be configured.