We have had a lot of feedback our Drupal site is running very slow on a different network. Most users on this network use IE (ie6 and ie8) which is causing a huge slow down compared with Firefox.

However, even in Firefox it is still slower than what we would expect. We have put this down to a local DNS issue (the DNS request is timing out after 2 seconds, then works off another DNS sever. I am assuming this is adding a 2 second latency to all page loads?)

What else might be problem here which is causing a dramatic slow down for Drupal only in IE?

Site in FF from YSlow: Empty Cache = Total Weight - 586.2K Primed Cache = Total Weight - 267.3K