condar,
There have been some ideas already from the chatterbox. Here is an idea that I had while I was thinking about it:

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

my %data;
my $file = $ARGV[0] or die "Usage: $0 <input_file>";
open(my $fh, '<', $file) or die "Unable to open '$file' for reading: $
+!";

my $pos = tell $fh;
while (<$fh>) {
    my $size = (split /\t/)[2];
    $data{$size} = exists $data{$size}
              ? $data{$size} . ":$pos"
              : $pos;
    $pos = tell $fh;
}
for my $size (sort {$b <=> $a} keys %date) {
    for my $pos (split /:/, $data{$size}) {
        seek($fh, $pos, 0);
        my $line = <$fh>;
        print $line;
    }
}
[download]

Note: This code is untested an is not optimal. It was just an idea I had that you might want to try. It will output lines of files with the same size in the same order they appeared in the original file.

Inlined get_size() sub which was just a call to split. Also specified keys %date