It's not.  It used to be, but it's not now, with Tcl interpreters after 8.0.
[[Refer to objective evidence.]]  It's necessary to answer the question, though, because so many antique claims to that effect continue to circulate.



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Tcl is often somewhat slower than Perl for comparable operations.  Algorithms that match Perl's regular expressions well
generally favor Perl, sometimes by a large factor; a lot of work has gone into optimizing Perl's REs.




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[[Explain other penalties--correct Unicode and thread handling, ...]]



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Naive Tcl coders rarely understand the simple steps that boost [Tcl performance].  [[Explain
why this affects Tcl differentially.]]

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See http://www.equi4.com/md5/ for one example where Tcl is not that
much slower.

Perhaps [JCW] will update these tests to reflect the new md5 code...