For the most part, I believe it is realistic and economical for the grade breeder to use AI bulls ranked from the 50th to the 90th percentile. The average of young bulls being sampled in AI sampling programs is nearly certain to exceed the average of presently available AI bulls that rank below the 50th percentile. If young bulls are used, it is desirable to spread the risk, as even the best pedigreed young bull could be a bust. In closing, I would encourage you to use a group of bulls whose averages meet your goals. If you try to have every individual bull you select do it all, you will pay more than necessary for semen and probably end up terribly frustrated.
Bulls are like people.
They are all imperfect, all in different ways and to different degrees. A group of bulls, all having some imperfections, but whose averages will take the things you want to improve in the right direction, are attainable. I encourage you to adopt this kind of philosophy in selecting sires.