Carn Ex. Just 2 cents worth mate, where I believe you are on the right track is that with 40-60, you are already amongst the winners with this rule alone!!
But I still can't go beyond implementing my pet filters: racing within 21 days over less than 2000m, (unless 1st up over 1200 or less) and must have a win in exposed form, and carrying 60kg's or less and NOT ridden by a 3kg's apprentice.

I've got more but THEY are the gospel, but Fillies and Mares races or Fillies only are really suspect in my view!