I think the ones that are really growing them rapidly are white Leghorns, but the could be white Plymouth rocks. I had one leghorn in the first group of 6, and got two more and the white rocks 5 days later. The rocks are slightly bigger than the leghorns I got at the same time, so it's a bit hard to tell, but I do think the rocks have a more delicate head shape. My wife is afraid that we might have one or two boys in there, but I hope there's none and some of the girls are just getting a comb sooner than the others.
I am 90% certain at this point that the one with the biggest comb is the leghorn we got with the original 6 birds. That group will be with us 2 weeks come Monday, so I'd guess they are about 2.5 weeks old now.
I'm not panicking at all, if we get some roosters we'll either give them away or feast on them.
My daughter's family has six of them and they lay a lot and big. We only have three, but we have two sex-links and two Golden Comets, and five other birds, so I think we'll have plenty of eggs, don't you?
Alaskan, you obviously have lots of experience with this breed, so I have a question. It seems to me (so far) that if they could, it would be these three girls who formed a biker gang... they are the rowdy ones in the brooder. Is that to be expected from this breed?