I have re-write rules in .htaccess to make sure that there is no switching between www. and non-www.
What I think may be the issue here is storing sessions in cache? I'm using Memcached and have added the following to my config file:
$config['cache']['cacheSessions'] = true;
We have anywhere between 70-85 registered members online (apart from 100's of guests), is sessions cache actually helping me or would I not notice a drop in performance even if I disable sessions cache?