Yes. By using FastCGI you will save the per-request initialization cost of running a normal CGI. This includes the time it takes to load the Perl interpreter and the time it takes to compile your script. In terms of performance enhancement FastCGI offers basically the same speedup as mod_perl. However, mod_perl also allows you to access the Apache API which gives you a whole load of capabilities that are not available in CGI or FastCGI.

-sam