...
use Benchmark qw(:all);
our $bruteforce_re = 0; # give it the extra preparation bonus

my $grinder = sub {
   my $fails = 0;
   for( 0 .. 10000 ) {
      ++$fails if ! /^(?:2(?:[6-9]|5[0-5]?|[0-4]\d?)?|[3-9]\d?|1(?:\d\d?)?|0)$/o
   }
   die "grinder $fails:" if $fails != 10000-2566    # did we get this right?
};

my $mwah = sub {
   my $fails = 0;
   my $re = qr{^(\d+)$(??{$1<=2566?'':'(?!)'})}x;
   for( 0 .. 10000 ) {
      ++$fails if  ! /$re/
   }
   die "mwah $fails:" if $fails != 10000-2566       # did we get this right?
};

my $bruteforce = sub {
   $bruteforce_re = '^(?:' . join('|', 0 .. 2566) . ')$' unless $bruteforce_re;
   my $fails = 0;
   for( 0 .. 10000 ) {
      ++$fails if  ! /$bruteforce_re/o
   }
   die "bruteforce $fails:" if $fails != 10000-2566 # did we get this right?
};

cmpthese(-3, {# grinder     => $grinder,
                mwah        => $mwah,
                brute_force => $bruteforce,
             });
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