Perl 5.8.0 is slow on your system because Red Hat compiled it with threads and debugging turned on (which you didn't do in your 5.8.5 compile) and because they set the locale to use unicode and folded in a bunch of patches for unicode that were not in the official 5.8.0 release. This has been written about extensively. See the Red Hat bugzilla for more details. This was fixed in 5.8.1. The remaining slowdown of 3.7 is probably due to the regex change that japhy mentioned.