You are absolutely right of course, but my point was that the hitch occurs when the skin isn't available, unless you mean the process of searching for the non existent skin on disk is causing the hitch? If that's the case wouldn't the conversion from full to compressed be far more resource intensive than a simple search? I have Full (as opposed to compressed skins) turned on, and available skins do not give any problems. It's only the missing skins that cause a hitch/stutter even with compressed turned on.
My thoughts are that the process of accessing LFSW, or some other agent (antivirus) might be slow and causing the interruption. For now I just set skin downloads to off and the problem is circumvented.