That a new extension would suddenly cause a performance increase is, as you rightly guessed, not true, unless the additional extension cause Windows to go through some additional hoops before it feeds the file to perl - not likely.

I've never seen a .pl*x extension before, but I have seen the .t extension. This is a test file, for testing modules, or the core.

Cheers,
Erik

Update: At tachyon's suggestion, I removed a guess about .pl*x extensions. As was correctly pointed out, if I didn't know, I should've kept my mouth shut.