speed of require/include

Hi everyone, I think this question is general PHP but because I'm using Windows for development at the moment and was wondering if it's related to Windows. Does the speed of require/require_once/include/include_once depends on disk activity, buffers (disks, controller, Windows)? I can't seem to get steady time from xdebug profile... it varies from 27ms to 170ms on one of my scripts while another script in the same framework with less require/include always have a steady ~6.5ms (the previous has 30 requires/includes and the latter has 8 requires/includes). I only have the skeleton of the framework for my project (no DB access, no fancy html/xml output). I'm running PHP 5.3.3 FastCGI on Windows 2008 R2 x64 w/ 4GB RAM. SATA RAID controller is 3ware 9650se. Thanks for your time, Tommy