You could use a package such as Tie::Array::Sorted to maintain a sorted array of your 10 highest scores (mapped to the corresponding code); once the array increases in size to above 10, just remove the lowest (last) item on the array as you go through the file.
The following needs a little refinement/ debugging, but shows an outline of how I think it should work....

use Tie::Array::Sorted;

tie @a, "Tie::Array::Sorted", sub { $_[0]->{score} <=> $_[1]->{score} 
+};

# read file line by line
while (<FH>) {
   # use split if you hate regexs... :-)
   if ( /((\d ){4})(\d.\d+)/) {
      # add new element to array
      push @a, { 'score' => $2, 'code' => $1 };
      # remove lowest scoring element if more than 10
      if ($#a > 10) {
          pop @a; # remove lowest scoring/last element
      }
   }

}
[download]