Below is result of benchmark in which none of the three transform subs print (to STDERR), instead they just return the array reference to the whole thing (sub transform{ return[ map{} sort{} map{} (list) ]; }).

URL Length Statistics:
  Total URLs: 1497  Lengths' Sum: 216277
  Min: 13  Max: 1270
  Mean: 144.474  Median: 62.000
  Std. Deviation: 234.977  Variance: 55214.052

Benchmark: running GRT, GRT UK, ST for at least 5 CPU seconds...
       GRT:  5 wallclock secs ( 5.05 usr +  0.01 sys =  5.06 CPU) @ 10.07/s (n=51)
    GRT UK:  5 wallclock secs ( 5.08 usr +  0.00 sys =  5.08 CPU) @  8.47/s (n=43)
        ST:  5 wallclock secs ( 5.27 usr +  0.00 sys =  5.27 CPU) @  7.79/s (n=41)
         Rate     ST GRT UK    GRT
ST     7.79/s     --    -8%   -23%
GRT UK 8.47/s     9%     --   -16%
GRT    10.1/s    29%    19%     --