Have you thought about Jersey Giants? They were originally developed as a dual purpose breed, with the intention of replacing the turkey. They take a little longer to reach full weight ... but that final weight can be pretty impressive. I've only got one at the moment (she's a Kindergarten dropout!) but so far, she's just about the sweetest pullet I've met, and I'm told they'll go broody, given the chance and some encouragement (a quiet nest box with a fake egg or two.) I'm seriously considering acquiring a roo next summer. They're a US developed breed, and endangered to boot and I think it would be fun to add them to my Nankins. Side-by-side runs with really BIG black chickens and really tiny red ones ... that ought to make for an interesting set-up!