Size of broilers: Are better foragers bigger?

I was curious whether my Light Sussex had been getting enough to eat on their strict diet.  I figured that if the combination of storebought feed and scavenged feed were below the optimal levels, we'd have a wide variation in chicken sizes --- some big ones that were able to forage best (or hog the feed) and some small ones who just couldn't find their own food.

One pullet seemed to support that hypothesis.  Even though we straightened out her foot as best we could, the chick born with curled toe stayed the runt, clocking in at a final dressed weight of only 0.87 pounds.  But she's not really a fair data point since I can envision how having only one foot to scratch with would slow a chicken down even under the best of conditions.  How did the other chickens do?

The chart below compares our poorly fed Light Sussex to our third batch of chicks, which were overfed in my opinion.  In both cases, I split the birds up into pullets and cockerels since the latter are naturally larger than the former.  I also deleted the curled toe pullet since she unfairly skewed the results.

I was interested to see that there was actually less variation in size among the Sussex than the Australorp cockerels.  The pullets showed more variation, perhaps because they are smaller than cockerels and thus got less of the storebought feed?  Or maybe the pullet variation was because of three hybrid pullets who clearly weren't purebred Light Sussex (they had gray instead of black neck markings) and who grew much faster than their sisters.

I was careful to select only the largest pullets and cockerel to keep as the foundation of our new flock, so hopefully that means I will have chosen the best foragers.  Maybe the next generation will have a feed conversion rate better than 5.3:1 at 12 weeks.  Yes, that means my darling Light Sussex didn't quite beat my spring Australorps, but they came close.