bannor:~/work/perl/monks$ perl 971240.pl 1000000
          s/iter  stunpack   stsubst plainsort
stunpack    12.4        --      -10%      -31%
stsubst     11.2       11%        --      -24%
plainsort   8.54       46%       31%        --

bannor:~/work/perl/monks$ cat 971240.pl
#!/usr/bin/env perl
use Modern::Perl;
use Benchmark qw(:all);

my @data;
push @data, int(rand(1000000000000))+10000000000000 for (1..$ARGV[0]);

cmpthese( 10, {
        'stunpack'        => \&stunpack,
        'stsubst'         => \&stsubst,
        'plainsort'       => \&plainsort,
});

sub plainsort {
    my @d = sort { 
        substr($b,0,8) <=> substr($a,0,8)
            or substr($a,8) <=> substr($b,8)
    } @data;
}

sub stsubst {
my @d =
    map { $_->[0] }
    sort { $b->[1] <=> $a->[1] or $a->[2] <=> $b->[2] }
    map { [ $_, substr( $_, 0, 8 ), substr( $_, 8)] }
    @data;
}

sub stunpack {
my @d =
    map { $_->[0] }
    sort { $b->[1] <=> $a->[1] or $a->[2] <=> $b->[2] }
    map { [ $_, unpack "a8a6" ] }
    @data;
}