I sample a page that's gets heavy usage and also has lots of images on it, this shows 70% of page load samples loaded between 1-3 seconds.
|mod_pagespeed with file cache|
After upgrading mod_pagespeed and enabling memcached, it now shows that 45% of page load samples loaded between 0-1 seconds and 41% between 1-3 seconds.
|mod_pagespeed with memcached enabled|
My memcached server stats