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use strict;
use warnings;
...
@output = sort { $b->[1] <=> $a->[1] } @output;

say sprintf('%s : length %s', $_->[0], $_->[1]) for @output[0..19];

use strict;
use warnings;
...

@long_seqs = sort { $b->[1] <=> $a->[1] } @long_seqs;
say  "$_->[0] : length $_->[1]" for @long_seqs[0..19];

use strict;
use warnings;
...

@long_seqs = sort { $b->[1] <=> $a->[1] } @long_seqs;
say  "$_->[0] : length $_->[1]" for @long_seqs[0..19];

77031 : length 351
52527 : length 340
...
56095 : length 322
80225 : length 320
81159 : length 320

   Nick's example:  1m32.958s real, 0m56.561s user - no caching
Laurent's example:  1m33.454s real, 1m00.491s user - no caching
Laurent's example:  0m18.761s real, 0m20.990s user -    caching