This is a great article comparing the performance of PHP on Windows and Linux & 5.2 versus 5.3 and asp.net on a Windows server. The testing methodology is very sound and well documented . But what I found just as interesting were the comments and which were well worth read.
Check it out here on the misfit guy website
UPDATE: The author has written another great follow up article taking on board feedback from devotees of PHP and ASP.NETÂ with more well written comments
Misfit guys follow up article