I'm having a PHP v5.3 web app running on IIS 7 which works correctly but sometimes the server reponse is very slow, normally the callback is about milliseconds and when it gets slow can reach to 20 secs.
I installed WinCache 1.0, configured output_buffering to On and print how long the PHP script last with microtime function.
This slow response is random, not everyday or in specific time and the number of users is limited.