Apache vs. IIS PHP performance comparison

PHP Best Practices article -- Differences between PHP on WIMP and PHP on LAMP

Some of the differences you may encounter when developing with PHP on Win/IIS vs Linux / Apache.

The most obvious difference between WIMP and LAMP is definitely performance.
For years there has been an obvious performance advantage of LAMP over WIMP.
Only recently is their even a chance of closing that gap.
There are currently 2 projects underway that may help.

Currently available is IIS7 which is reported to have had PHP performance enhancements built in with collaboration from the ZEND team.

An upcoming projects involves Microsoft engineers working with PHP engineers to get the next version of PHP (PHP5.3 which is not yet available at this time) to perform much better in IIS. This will no doubt make some progress toward WIMP catching up with LAMP in performance.

FastCGI on IIS will significantly increase the performance and will be comparable to that of LAMP. The difference will be in details, which are hard to pick and depends on what your configuration is and on what you scripts do. For example, file access on Windows is much slow than on Linux because of NTFS's ACL checks.

There is nothing particularly wrong with the Windows web stack. The only big reason I'd think of using Windows over Linux when human experience doesn't matter would be SQL Server. Otherwise WAMP, WIMP and LAMP perform comparably and performance differences won't show up until heavy load.