Very interesting: CGI::Simple states to be faster than CGI. So either this claim is not true or there is something else: perhaps CGI is preloaded by the server and CGI::Simple needs to be loaded again and again at the start of the script? If I have some time to spare during the next weekend, I might try some tests myself.
Update: I now only see that you are using the functional interface to CGI::Simple (i.e. CGI::Simple::Standard) and that the claims to be faster only relate to the OO-interface.
"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law