I don't know how many req/sec it is supposed to process. I saw sometimes 100 req/sec and 400 in processing, so it should be able to process more req/sec so that there wouldn't be 400 in processing making the site load so slow. When the in processing is low, the site can load in under 1 second, so I don't think the CGI script take a long time to process.
The server is running very smooth now since I tracked down the issue to MySQL.
Is there anything else I need to do to improve req/sec?