Windows XP with latests updates, 512MB RAM, Pentium 4 at 1.6GHz, and Apache 1.3.24, PHP 4.3.1 as a module and MySQL NT 4.0.12, AND Norton Personal Firewall activated:
Result: 303.17 seconds (1.52 seconds per call)
Worse than a very old Linux box with one fourth of the memory, a CPU about 4 times slower and a worse software. Linux Power!
Note that the kernel of Windows XP is even better than the one for Windows 2000 (both are NT sons).
Of course, all these comparisons are very relative, since each Moodle home page is different and has a different number of selects to make. Anyway, mine are similar, and the fastest one is also the biggest