You say it all in your last (body) paragraph:

Is it safe to assume that undef heavy usage, say, a popular website driven by some cgi, the safe way of doing stuff will not cost more, or reduce responsiveness?

Under heavy usage, when speed is important, don't use objects when they don't clear things up by a large bit, like here. Instead, use hashrefs, which are much cheaper then either a method or function call. However, your apositive gives you away. Don't assume that's a matter of your CGI being slow. And even if it is, don't assume that the best way to do is to make the script harder to read. Instead, going to mod_perl will have more benifit for lest cost.

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