No fair changing the initialization code. It can't be change since the OP's modification was done in-place.

   zen3 => 'my $mac = $data; $mac = ":" . $data . ":";
                             $mac =~ s/(?<=:)(?=[0-9a-fA-F](?::))/0/g;
                             $mac =~ s/^:|:$//; $mac;',

   zen4 => 'my $mac = $data; $mac = ":$data:";
                             $mac =~ s/(?<=:)(?=[0-9a-fA-F](?::))/0/g;
                             $mac =~ s/^:|:$//; $mac;',

   zen5 => 'my $mac = $data; $mac = ":$data:";
                             $mac =~ s/(?<=:)(?=[0-9a-fA-F](?::))/0/g;
                             $mac = substr $mac, 1,-1; $mac;',
[download]

Fixing that didn't affect the result, however.

             Rate jwkrahn1 skeeve jwkrahn2 ike_orig ike_fast   zen4   
+zen3  zen5
jwkrahn1  62625/s       --    -4%      -4%     -12%     -36%   -42%   
+-43%  -44%
skeeve    65186/s       4%     --      -0%      -8%     -33%   -40%   
+-40%  -42%
jwkrahn2  65395/s       4%     0%       --      -8%     -33%   -40%   
+-40%  -42%
ike_orig  71122/s      14%     9%       9%       --     -27%   -34%   
+-35%  -37%
ike_fast  97408/s      56%    49%      49%      37%       --   -10%   
+-11%  -13%
zen4     108516/s      73%    66%      66%      53%      11%     --   
+ -1%   -4%
zen3     109083/s      74%    67%      67%      53%      12%     1%   
+  --   -3%
zen5     112484/s      80%    73%      72%      58%      15%     4%   
+  3%    --
[download]

Your three are equally fast, and slightly faster than the previous best.