You could try to minimize the difference with:

 => where {
          /^$RE{zip}{US}{-extended => "allow"}$/o
      };
[download]

Here on linux with perl 5.10 it gives:

    Rate    A    B
A 2402/s   -- -22%
B 3080/s  28%   --

The original benchmarked as:

    Rate    A    B
A 1851/s   -- -39%
B 3024/s  63%   --

Best regards