I am experiencing similar problems, although perhaps not as severe. (cosmaprof.net)
For some reason it takes a good 20 seconds before any of the browsers I have used start loading the page. It seems it’s waiting this long for the request and than the page just “boom” suddenly appears in a matter of seconds.
However, (now comes the kick) this only happens when I am logged in. If I am logged out everything seems to load very fast indeed.
Any idea what the root of this problem and how I can resolve this. I mean my website is designed to let people register and subsequently have to login to leave comments and such.