Well that is the age old question.....
I have seen some "cull" dogs throw some awesome cow dogs and hog dogs....and I have seen some champion (literally on both sides) dogs throw some junk....... It isn't an exact science...... it really depends on how much time is being put into the pups and how they are treated. You sometimes have to try different crosses to get a good dog. Just because they are proven dogs doesn't mean they will have proven progeny. That goes for dogs, horses, catlle and even people.......
Having said that...... I personally would not breed two dogs that didn't posess some traits I am looking for in a dog.