Actually constants are faster, since use constant simply turns them into constant subs (for versions of Perl that support this):

sub CONST_NAME () { 'value' }
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IIRC, this form is optimized by the Perl compiler such that there are no hits to the symbol table in dereferencing the value; it would be as if you typed the constant value in as a literal, much like a preprocessor #DEFINE macro.

update: Looks like I was wrong, my variables are actually a hair faster than both constants and even literal values.

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print