This doen't looks like CGI::POST_MAX limit. (judging by CGI.pm doc, it have to output error 413 "Request entity too large"
Rather this is simply timeout in your browser :)
And to solve this you have to upgrade your bandwidth ;)
Yep, turned out it was the Apache Timeout.. Upped that value so that it wouldn't time out after 5 minutes and managed to push up the entire file.
Thanks for the info :)