Why not just write to a dummy file. I kind of like this a hair better than writting to dev null or monkeying around with stdout. This would be a very fast change.

open my $fh, '>','delete.this.later' or die ("Unable to open temp file
+ : $!");
...
my $result = timethese ( -5, {
   test => sub { print $fh @A },
...
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And then just delete the file afterword. Sure you'll introduce a bit of Disk IO, but it's the same DiskIO for all of your test threads, so it should wash out in terms of a comparison.