I found the Buckeye breed excellent for roasting the young cocks (got them to table a little early as had to process early due to new grand baby speeding up my time line). Even so, they had a healthy amount of meat on the breast.
I also that year had Rhodebars which were amazingly good for laying, and the young cocks too were good for roasting. Nice thing about the Rhodebars is they are autosexing which means at hatch you can designate proper feed programs for girls vs. boys.
I agree that anything that gets beyond 6 to 8 months of age is best in the soup pot or casserole. You also won't get the proportions you expect form the Cornish Cross roasters to meat, especially breast. Though the Buckeyes come about as close.
If you want a truly dual purpose bird, I highly recommend the Buckeye. Sweet docile birds, decent layers (better if you get from a higher lay line). Boys are nice tempered and come to table earlier than most...even fast if you feed them along meat bird schedule. (But obviously no where near as fast as they hybrid Cornish Cross which comes to table by 8 weeks). I agree get birds from a breeder rather than a hatchery.
I have loved my Marans, though I have not eaten them. They are too valuable for my breeding program for egg color, carrying the dark brown genes for me. I've either sold my cocks or returned the hens to breeding program or sold them off. But they do have a heavier carcass. My Marans have been very broody. I now have only birds I've bred and raised on my property, about 3rd to 4th generation down. Every hen that has any Marans blood has been a good brooding hen.
Just some breed comments.
And yes...WELCOME to BYC....I failed to notice you are a new poster

LofMC