I've raised too many Cornish X to count at this point and done most of my processing at 8-10 weeks but I've also let a few go to 12 weeks. Mine start in a Rubbermaid 120 gallon water trough brooder, then move to a 6'x12' tractor at 3 weeks old. After that, I move them to another tractor which opens to a half acre fenced pasture; I give them access to feed but I move the feeder and waterer every time I fill them so that they have to move to get fed, and so they don't cake up one single area with poop. The coop has a 2"x4" laid on its side on the floor as a "roost bar"- they just have to step up on it to roost and they don't have to risk breaking a leg or pulling a tendon jumping down off anything high. They seem to appreciate the width of the board for their giant clown feet and big bellies.
It's hard to remember that these full sized behemoths are still just chicks when it's time for them to be sent to Camp Frigidaire.
I also have tried out Atwood's Red Broilers and Black Broilers, I reckon they're similar to the Red Rangers. I raise them the same way and basically on the same timeframe with the exception that they stay much longer on the half acre to size up, they'll reach 6-7lbs in 12-14 weeks. They're also much more willing to forage, too.
My biggest complaints on the Red and Black Broilers are the longer time to processing day and, more than that, the little red and black pinfeathers that make the carcass look messy. They're delicious, though. IMO, better flavor than the Cornish Xs.