I'm trying to get and keep my mature cows in the 1200 lb range. Using a moderate size registered bull with good calving ease (CED), moderate mature cow weight (MCW) and very high marbling (MARB) epds, I look for 1200 lb cows that will wean 205 day calves at 600-650 lb on good grass. I do leave the calves on the cows longer than 205 days but Cattlemax adusts weaning weights back to standard. The AHA mature cow weight epd is very useful if you are  trying to reduce cow size..

I think there is much more to right (efficient) sizing cows than just bull frame score.