Difference between FastCgiExternalServer and FastCgiServer in Apache FastCGI PHP?
FastCgiServer is a server that mod_fastcgi will do process management for -- spinning instances up and down and giving them a unix domain socket to listen on. No outside action is required to start the fastcgi server.
FastCgiExternalServer is a server that mod_fastcgi will NOT do any process management for -- it will just reach out to the unix or TCP socket you tell it to use and forward requests/responses to it. You, or some daemon outside of httpd, must be starting something to listen on the listed socket. The most basic way is the 'fcgistarter' utility, other options are things like php-fpm.
If performance is reason, I would say use Apache with fcgid. This is considered better for performance.To deal with performance, mod_fcgid starts multiple instances of CGI programs to handle concurrent requests. This is alternate to mod_php for PHP developers, giving higher performance. This article I found is great resource to learn
http://2bits.com/articles/apache-fcgid-acceptable-performance-and-better-resource-utilization.html