We fed our 10 cornish rocks 22.5% protein broiler ration the whole 6 weeks and butchered them right at 6 weeks. They weighed 4.5-5 pounds each dressed weight. I think I have seen the suggestion to drop back to 18-20% around 6 weeks but if we had done that we would have ended up with 8 pound birds at 9-10 weeks and I didn't want them any bigger than they already were. They are deceptively large. I was surprised at their weights. At some point, all they are putting on is fat. You might butcher one now and see if you like the way it is. That way you can determine whether to continue feeding as you are, change to lower protein or go ahead and put them all in the freezer. It seems to me that people have varying results depending on how they feed and how much exercise the birds get. Mine were rather confined, but I have an idea that if they had had more space they would have still fallen asleep with their beaks in the bowl. They are tremendously lazy.