print is indeed fast when the open fails :) Trying with:

use File::Spec;
open my $zap, ">", File::Spec->devnull or die "open failed: $!";
use Benchmark "cmpthese";
cmpthese -10, {
   every => sub { for (1..100) { print $zap $_ } },
   tens  => sub { my $x;
                  for (1..100) {
                    $x .= $_;
                    unless ($x % 10) {
                      print $zap $x;
                      $x="";
                    }
                  }
                  print $zap $x if length $x;
                },
}
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on first ActivePerl build 811, then cygwin perl 5.8.6 (the latter being a debugging build):

$ aperl nullout.pl
        Rate every  tens
every 3792/s    --  -34%
tens  5728/s   51%    --

$ perl nullout.pl
        Rate every  tens
every 1479/s    --  -54%
tens  3226/s  118%    --
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