We did the cornish roasters as our first batch of meat chickens. We currently have a batch of Colored Rangers. Our Cornish Roasters grew well - the roosters dressed out at 6+ lbs. at 7 weeks, and the hens were 5+ lbs. at 8 weeks. We didn't loose any nor did we have any leg or heart problems. Although, by the end, the bigger roosters definitely had trouble moving from one side of the pen to the other. Not leg problems, but they would have to flap their wings to help them get any further than a few feet.