Thanks for everyone's suggestions.
One of the reason I waited to get them until 9/25 is that it is normally fairly cool here by the end of October. We started October with highs in the mid-90s, but now we're at highs in the mid-70s (although we only had a high of 64 this weekend), and lows in the mid-40's. There were enough warnings on this site about trying to raise Cornish Xs in the heat that I knew I'd have to wait.
I have the feeders raised at the right height; it's more of a pushing/shoving match, but it only happens when they run out of food. I think the key to Simplicity's big birds is the food restriction, but I also think Greyfield has a point that some are just destined to die earlier than others.
I do like the idea to get more feeding area; I'll have to move them to a larger tractor. I don't think I was as prepared as I thought I was, for how much space 30 chicks take up! Silkie, isn't it a pain to always be raising chicks? I find they are much more labor-intensive than my hens or my dogs. Also, with so few chicks, I would be afraid I would get attached to them; this bunch of chicks is just a big mass of meat on feet, and no one stands out as a personality. For me to process and eat them, that's probably the way it has to be. That's the same rationale that prevents me from shooting the "house deer"; I have to go scout out locations where deer I don't "know" hang out!
Just to reiterate other people's comments, this is a wonderful site and I really appreciate ya'll. On evenings when I have no other time to spare, even to check email, I at least check this site!