I think this is a case of premature optimization. The length of symbols used in a program should only be an issue during compilation. In general, once the program has started, it shouldn't matter.

In Perl I know of only two ways in which symbol lengths can affect execution. One is evaling a string (don't do that), which invokes the compiler again, and the other is using symbolic references (don't do that either), which use strict forbids.

If you have a CGI program that's being compiled every time it executes you might want to look at converting it to mod_perl.