I have during the last months been fighting to get a better response time on my site until I stumbled upon this one:
From the webside:
This tool lets you test web pages that are directly accessible as an URL from the Internet. If you need to test a page inside of a firewall or something more complicated than a web page (an authenticated product like webmail for example) please download the desktop version of PageTest which this is based on.
It was very interesting , and after performing the test a few times (from different servers), the response time went down from (worst case) 17 seconds to 4 seconds after a few mods to my WordPress installation. I am not trying to say that this solution is the one and only, or the best one. This is just something that worked for me.
I will return with more detailed info in a few days.