We've done a benchmark of mod_perl / FastCGI against regular CGIs, and the results where roughly that the same script runs around twice as fast under mod_perl or FastCGI than as a CGI. These results were got without changing the CGI at all, i.e. they might even get better if you tweak the script to take advantage of special characteristics of mod_perl and FastCGI. These two seem to offer similar performances.