>perl -wMstrict -le
"use Benchmark qw(cmpthese);
 my %HASH;
 my $not_key = 'not_key';
 $HASH{ rand() } = 1;
 compare();
 $HASH{ rand() } = 1 for 0 .. 30_000;
 compare();
 sub compare {
   print '------------------';
   print 'hash keys/buckets: ' . %HASH;
   my ($is_key) = each %HASH;
   ! exists $HASH{$not_key} or die qq{$not_key should not exist};
     exists $HASH{$is_key}  or die qq{$is_key should exist};
   print qq{test keys '$is_key' and '$not_key' seem ok};
   my $HR = \%HASH;
   cmpthese(-2, {
     hash_hit  => sub { exists $HASH{$is_key}  },
     hash_miss => sub { exists $HASH{$not_key} },
     href_hit  => sub { exists $HR->{$is_key}  },
     href_miss => sub { exists $HR->{$not_key} },
     });
   }
"
------------------
hash keys/buckets: 1/8
test keys '0.408477783203125' and 'not_key' seem ok
               Rate hash_miss href_miss  href_hit  hash_hit
hash_miss 3305141/s        --       -6%      -22%      -42%
href_miss 3520236/s        7%        --      -16%      -39%
href_hit  4215045/s       28%       20%        --      -27%
hash_hit  5746274/s       74%       63%       36%        --
------------------
hash keys/buckets: 14778/32768
test keys '0.091217041015625' and 'not_key' seem ok
               Rate href_miss  href_hit hash_miss  hash_hit
href_miss 3392515/s        --      -18%      -21%      -36%
href_hit  4126900/s       22%        --       -3%      -23%
hash_miss 4272362/s       26%        4%        --      -20%
hash_hit  5329295/s       57%       29%       25%        --