Optimization is highly use-case dependent. If a particular use case dictates that the difference between the invocation weight of backticks, open, IPC::Open3, pipe/fork/exec or any other flavor of external call will be problematic, then it's reasonably likely Perl is a bad choice of context. Perl is a great choice of language for optimizing programmer vs. computer times, and generally timing doesn't really matter as long as global execution time is less than a second. But even the most diehard adherent should be willing to question whether they've chosen the right tool for the job at hand.