Without looking, I'd bet that there are one or more subsection of each that are not used by every use of the main module and that these could be factored out into sub module(s) and required when required rather than loading everything always.

CGI.pm certainly could do this, even allowing for the fact that it generates a lot of it's function on demand. I fully understand the motivations and temptations for people that want to "just parse the options string and print a header or two". If the major :xxx load options to CGI.pm effectively turned into

require 'CGI::HTML4' if %opts{ html4 };
require 'CGI::download' if $opts{ download };
[download]

I don't think it would do any harm at all.

The only downside of that is that Perl doesn't support a use Foo::*; syntax, though writing a use wild 'Foo::*'; pragma would be possible I think.

I have a general preference for lots of small files, rather than 1 or 2 huge ones. With editors that can hold multiple files and provide search/replace/index across all workspaces, I find the ability to be working in several places at once in different files very useful. My editor also supports having multiple views of a single file, but I very rarely use it. Years ago I used a very excellent folding editor which encouraged you to put lots of stuff in a single file and use a collapsed view to navigate. It worked great, but then compiling became a chore.

I like to keep as much as possible to do with one unit of code in the same file as I can. Code. Interface (user) docs. Breif modification history. Unit tests. This becomes unweildy where the units are too all encompassing.

For a very large OO module, I would seriously consider putting the class definition, initialisation, constructors and destructors into one file and moving the methods into one or more separate files and loading them as procedures.

Anyway, it's just a preference, not an edict. The OP will doubtless make up there own mind on the matter.