Barred Plymouth Rock in current stock are notoriously slow to mature. They never were speedy but over a hundred years from origin and these have gotten worse. White Plymouth would be a better choice. It's the best variety of that breed. White birds will present better table bird. Dark pin feathers can be unsightly to some.
Buff Orpington, it's England's Plymouth Rock. The birds are very similar from conception, Plymouth was the back bone of it's foundation breeds. Orps of today have a lot of poof to feathers. That's different. They may or may not get as large as a White Rock as they are outer edge to over breed standard. All in all, it's apples to apples.
New Hampshire. Now here is a bird that was made by intensive selection of the fastest maturing Rhode Island Reds. That's it's founding breed. No other. It's a 20th Century bird and geared for broiler industry use. I'd don't think I need to say much more on that. Does it perform as it did in the 50's? No but it's the best standard bred performer going I can find. Not hatchery birds though, those are production reds and not New Hampshire no matter what they tell you. If you want a true dual purpose bird and New Hampshire find a breeder and get stock or eggs that way.
Buckeye is promising. Take note on page 7 in this link. Live weights of cockerels in 16 weeks of 6 lbs. 66% would be a good percent to estimate carcass weight. Good link for showing selecting breeders to keep whatever you choose for breed in a meat oriented utility bird.
Hatcheries picked up on the piqued interest in Buckeye due to the conservation effort. For ease of getting a good dual purpose bird that will still perform well....they've only had them a few years now so may not have turned them into strictly layers yet. Imagine you can get good stock still from hatcheries. They purchased conservation birds to get in on the attention the breed was/is getting so may still be good stock at bargain price.
Edited by Egghead_Jr - 2/5/16 at 7:41pm