I tried to get more information about the speed of AjaxPro calls on my web site. First of all I did a research on how the latency of internet connection will change the duration. For this I run a test for my web server at http://just-ping.com/ . You will see that Nürnberg, Germany will be always the fastest because it is located near to my web servers location.
Then I started to log some example requests I'm currently running on http://www.ajaxpro.info/ . If you are opening this page 10 requests will be done to the web server using AjaxPro. The duration will be captured on the client side including other stuff like "window.setTimeout" (which will need more time on slower machines).