Why separate? A chicken is a chicken. The heritage Barred Rock hens I raised for meat were in with the layers. Everyone eating 18% protein for health, grass and all the bugs they could find. Most important part is size. Same size, no issues. If difference, then the big ones eat and bully the little ones into giving up on their share. The CX get big quick. The lesson here is provide enough space and feeding stations for all to eat. If in a coop or tractor, yes separate for size for optimal growth.
Ma-mom raised free feed store birds. Mostly leghorns. When eating time came, leghorn it was. Always had a fresh supply. They would go broody and bring in babies. She only free ranged and shot every predator that stuck its nose out. Go Grandma!