Splitting your script only helps if the startup time of the script hurts, and splitting it means that you need to load fewer modules in each script.

Here are some general tips for speeding up CGI scripts:

• Use a profiler to identify the slow parts; that way you don't waste your time speeding up things that are already reasonably fast (you will, without profiling)
• Cache whatever you can, avoid recomputations. Cache::Cache is easy to use, for larger scaling memcached might be interesting
• Save startup time by using persistent processes (FastCGI/mod_perl/others);
• Generate some pages statically (that's a form of caching too)
• If you use a relational database, check if all necessary indexes are in place
• Place some ads on your pages and use the income to pay for better hardware