mod_fastcgi (www.fastcgi.com) is a 3rd-party module whose directives have a "FastCgi" prefix.
mod_fcgid http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html is an Apache module whose directives have a "Fcgid" prefix.
I advise that you remove mod_fastcgi and go with mod_fcgid.
That's great news for PHP, because then you can dump apache mpm-prefork and go with the better mpm-worker, by not installing mod_php, instead use php as fast cgi. For debian, this means:
• Remove apache2-mpm-prefork and libapache2-mod-php5.
• Add apache2-mpm-worker, libapache2-mod-fcgid, and php5-cgi. With php5-cgi, you don't need a custom fast cgi wrapper, you can use the php command-line itself directly (notice the /usr/lib/cgi-bin/php5) below.
• For mod_fcgid with PHP, note that PHP as FastCGI has its own facility for terminating after handling so many requests (see PHP_FCGI_MAX_REQUESTS). FcgidMaxRequestsPerProcess helps avoid sending additional requests to the wrapper application after it has handled its limit.
• Inside each virtual host or at global scope:
FcgidInitialEnv PHP_FCGI_MAX_REQUESTS 200
• Then inside Directory:
AddHandler fcgid-script .php
FcgidWrapper /usr/lib/cgi-bin/php5 .php