...
    cmpthese -1, {
        full    => q[scalar keys %full,  ++$i for 1 .. 10000],
        empty   => q[scalar keys %empty, ++$i for 1 .. 10000],
        fake    => q[scalar keys %full,  ++$i for 1 .. 10000],
    }
}
__END__

Length 2 with 22/32items
       Rate  fake empty  full
fake  403/s    --   -2%   -3%
empty 411/s    2%    --   -2%
full  417/s    4%    2%    --

Length 3 with 510/1024items
       Rate  fake  full empty
fake  415/s    --   -1%   -1%
full  418/s    1%    --   -0%
empty 419/s    1%    0%    --

Length 4 with 13961/32768items
       Rate  full empty  fake
full  406/s    --   -2%   -2%
empty 414/s    2%    --    0%
fake  414/s    2%    0%    --

Length 5 with 310721/524288items
       Rate  fake  full empty
fake  406/s    --   -0%   -1%
full  407/s    0%    --   -1%
empty 411/s    1%    1%    --

Length 6 with 8655839/16777216items
       Rate  fake  full empty
fake  400/s    --   -3%   -3%
full  411/s    3%    --   -0%
empty 411/s    3%    0%    --