$ perl ref_cmp.pl
Benchmark: running numbers 2, numbers 4, qrefs 2, qrefs 4, refs 2, refs 4, strings 2, strings 4, each for at least 3 CPU seconds...
 numbers 2:  4 wallclock secs ( 3.08 usr +  0.00 sys =  3.08 CPU) @ 740880.04/s (n=2278947)
 numbers 4:  5 wallclock secs ( 3.18 usr +  0.03 sys =  3.21 CPU) @ 497290.48/s (n=1593816)
   qrefs 2:  3 wallclock secs ( 3.08 usr + -0.01 sys =  3.07 CPU) @ 640138.26/s (n=1967785)
   qrefs 4:  4 wallclock secs ( 3.02 usr +  0.00 sys =  3.02 CPU) @ 428683.86/s (n=1296340)
    refs 2:  4 wallclock secs ( 3.11 usr +  0.01 sys =  3.12 CPU) @ 414780.49/s (n=1292456)
    refs 4:  5 wallclock secs ( 3.02 usr +  0.01 sys =  3.03 CPU) @ 280746.21/s (n=851784)
 strings 2:  3 wallclock secs ( 3.06 usr +  0.02 sys =  3.08 CPU) @ 642239.02/s (n=1974885)
 strings 4:  4 wallclock secs ( 3.11 usr +  0.01 sys =  3.12 CPU) @ 476537.87/s (n=1484892)
              Rate refs 4 refs 2 qrefs 4 strings 4 numbers 4 qrefs 2 strings 2 numbers 2
refs 4    280746/s     --   -32%    -35%      -41%      -44%    -56%      -56%      -62%
refs 2    414780/s    48%     --     -3%      -13%      -17%    -35%      -35%      -44%
qrefs 4   428684/s    53%     3%      --      -10%      -14%    -33%      -33%      -42%
strings 4 476538/s    70%    15%     11%        --       -4%    -26%      -26%      -36%
numbers 4 497290/s    77%    20%     16%        4%        --    -22%      -23%      -33%
qrefs 2   640138/s   128%    54%     49%       34%       29%      --       -0%      -14%
strings 2 642239/s   129%    55%     50%       35%       29%      0%        --      -13%
numbers 2 740880/s   164%    79%     73%       55%       49%     16%       15%        --