You forgot to include the solution I provided! And let's include a basic use of sort to see what that looks like and how the others compare to that.

          Rate   basic     GRT      ST keysort
basic   1.66/s      --    -88%    -89%    -91%
GRT     13.3/s    701%      --    -12%    -25%
ST      15.1/s    810%     14%      --    -15%
keysort 17.7/s    972%     34%     18%      --

          Rate   basic     GRT      ST keysort
basic   1.79/s      --    -87%    -89%    -91%
GRT     13.5/s    654%      --    -15%    -30%
ST      15.8/s    786%     18%      --    -18%
keysort 19.3/s    980%     43%     22%      --

          Rate   basic     GRT      ST keysort
basic   1.70/s      --    -87%    -89%    -91%
GRT     13.3/s    681%      --    -15%    -27%
ST      15.6/s    817%     17%      --    -14%
keysort 18.3/s    972%     37%     17%      --
[download]

Sort::Key isn't only the cleanest and simplest of all the solutions (including the builtin sort), it's the fastest! It's 17-22% faster than the next fastest.

#!/usr/bin/perl
use strict;
use warnings;

use Benchmark     qw( cmpthese );
use File::Slurper qw( read_text );
use Sort::Key     qw( rikeysort );


my @unsorted =
   split /^(?=>>> )/m,
      read_text( "try3.txt" );

@unsorted = ( @unsorted ) x 10_000; # 90_000 lines (30_000 records)


sub basic {
   my @sorted =
      sort {
         my ( $an ) = $a =~ /(\d+)%/;
         my ( $bn ) = $b =~ /(\d+)%/;
         $bn <=> $an
      }
         @unsorted;
}


sub ST {
   my @sorted =
      map $_->[0],
         sort { $b->[1] <=> $a->[1] }
            map [ $_, /(\d+)%/ ],
               @unsorted;
}


sub GRT {
   my @sorted =
       map substr( $_, 4 ),
          sort
             map {
                /(\d+)%/
                ? ( ~ pack( "N", $1 ) . $_ )
                : ()
             }
                @unsorted;
}


sub keysort {
   my @sorted = rikeysort { ( /(\d+)%/ )[0] } @unsorted;
}


cmpthese( -3, {
    basic   => \&basic,
    ST      => \&ST,
    GRT     => \&GRT,
    keysort => \&keysort,
} );
[download]

Note: I found substr( $_, 4 ) to be slightly faster than unpack( "xa4", $_ ), thus the change in GRT.

Regexes ARE slow (of course everyone here knows). To the extent I can trust my Strawberries and/or my crippled Kaby Lake to benchmark anything, the next is twice as fast (+ I guess rnkeysort should have been used (and it's slower)):

sub keysort1 {
   my @sorted = rnkeysort { substr $_, rindex( $_, '%' ) - 3, 3 } @uns
+orted;
}
[download]

And assuming $s keeps the (un|pre)split input, and if each 2nd '%' is guaranteed to be an anchor, even if records have different length/layout, then the next unclean ugly one is still faster than keysort for me:

sub test1 {
    my $i = my $j = 0;
    my @nums;
    $j ^= 1 or push @nums, substr $s, $i - 3, 3
        while -1 != ( $i = index $s, '%', $i + 1 );
    my @sorted = @unsorted
        [ sort { $nums[$b] <=> $nums[$a] } 0 .. $#nums ]
}

__END__

          Rate keysort   test1
keysort 21.6/s      --    -30%
test1   30.6/s     42%      --
[download]