web service performance differences between Winform and Silverlight

Question

post http://silverlight.net/forums/t/119249.aspx explains how to improve request- response performance for concurrent WCF calls. I have a problem using sequential calls; result of a previous call are used in the next call started in the completed handler. It cost max ~100ms to start the next call when the previous is finished (measured using Wireshark).

Testing using a Winform application using the same asynchronous webservice methods, result in a much lower delay between 2 calls  (request-response time delays are similar).

Does anybody have some suggestion to improve this Silverlight performance?