I just finished trying out PerlEx for speeding up some legacy CGI stuff on IIS. It worked great: about 800% speed improvement with no code changes. Easy to set up.

If you haven't coded for mod_perl or fastCGI before you will have a little transition to deal with. You have to get used to writing cleaner code with lexicals and avoid slurping huge chunks of data into RAM. The docs should cover most of it.