Here's my little personal joomla site: http://shockadvised.net
This is completely running on Windows 2003/IIS6 with mySQL5 and PHP5 (although mySQL 4 and PHP4 produce identical results). In my opinion this is pretty quick. At one time, we had issues with the site running slow, and it turned out after a few days of trying to figure it out, that it was a disk I/O intense program running (real-time virus scanning) causing php/mySQL sites more than ASP.net sites to run like molasses. I would make sure nothing is hitting disk I/O too hard in task manager.