One thing to watch for is that the hatcheries only guarantee 90% accurate sexing for a reason. It is hard even for a professional to get it right all the time. You probably have a few pullets in your flock. If you have 100% males, the fighting will be pecking order fighting and no worse than having all pullets, but with pullets in there, it can be flock dominance fighting, which can be worse. Barred Rock are not sex links so you really can't tell by looking when they are young, but the pullets tend to be darker than the males. When they are raised together, the roosters often work out the dominance issues without serious fighting, even with pullets in the flock with them, but sometimes they don't. You may want to watch and pull your pullets out and separate them from the cockerels once you are sure of sex. It will reduce fighting.
I don't weigh my birds, but I do find a pretty big difference in size amoung individuals, especially in hatchery birds. To maximize growth, you will need to keep food out at all times.
Good luck!