I would reach into the toolbox for sort, and do:

sort -n -r -k 3 file -o outfile
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sort numerically, reversed, on the third key, write into outfile.

and in perl:

my @args = qw/ sort -n -r -k 3 file -o outfile /;
system( @args ) == 0
  or die "something went wrong with: @args: $?\n";
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