This is a thought and hopefully someone can clarify this for me as its only an assumption, but, I bought Cornish X and they were all cockerals. Now with the machine "eviseration" (hope that is right), they may want the pullets due to the need for removing the immiture male parts that lay on the back bone.
I was always told that if they stay, it makes the meat taste bad, and trust me, they are not easy to chase when processing! (hee hee).
Pullets are smaller then cockrals, but the cockrals may be easier to show signs of growth for fair season.
As for uniform size, I dressed off 10 "roasters" that were from 5 1/4 to 5 1/2 lbs at 6 weeks. Not weighing prior to processing, I would still assume that they would be the same approx size feathered.
I guess I'd rather have cockrals for the freezer because they gain much faster and its less time you have to put into it. As for food, larger size means more food regardless to age (IMO).