If you are interested how the PHP engine is evolving for the Windows Server platform, I would recommend to look at this article. I must admit that there have been major improvements in the PHP engine and I do believe running PHP in IIS is the way to go. Just to copy some improvements listed:

• Recompiled PHP with Visual C++ v 9.0, which improved the performance of the PHP core significantly.
• Both 32bit and 64bit builds (64 bit builds experimental until PHP 5.4/6.0) of PHP have been made available.
• Optimized the PHP implementation to take advantage of native Win32 APIs, instead of relying on POSIX emulation libraries
• Fixed the standard PHP test suite, which now has a much higher pass rate on Windows Server
• All PHP libraries have been fixed to be built from the source code. 10 years old libraries have been updated to newest versions.
• Build environment for PHP on Windows Server has been standardized and now it is easy for anyone to rebuild the exact same PHP stack on Windows Server as the release build.

To stay updated on the PHP on Windows news, you can check the IIS PHP portal or the PHP for Windows site.