just a note...
Apache2 is supposed to be more stable on win32 NOT faster, and I find it is exactly that ,not faster though it is supposed to do better under load than apache1.* which is not even recommended for win32 + of course PHP4/Apache2 is still experimental and as such quirky.
PHP can run as an ISAPI module on IIS , not sure for sure about the speed difference, MS admit that any server module would probably be faster than say vanilla ASP but of course .NET is a different cookie altogether from that.
But whilst I would love to see a speed fest between the 2 I dont think its realistic to really compare PHP (or PERL/Python/whatever for that matter) on IIS, whatever the result there will always be the 'ah but try it on *NIX factor' possibly from the likes of me even in a `win` situation.
Different databases is as much the key as anything, MySQL excels (as already noted) on straight selects and therefore would be expected to win vs SQL server on the simple stuff , but since MySQL is x-platform you could use that for both? , or Oracle if anyone has a spare liscence (or home edition [haha])