We actually order from a local hatchery some birds that they call a "plymouth rock" line. They pretty much look like cornish x to me but they do take 10 weeks to grow out, are much more active than the cornish rock x we've had in the past. The cuckoo marans I processed was 5.24lbs. Based on that I'd rather raise marans for meat than Delawares at this point. We shall see.The buying group where I sell eggs did pre-sale of Heritage Breed Turkeys for Thanksgiving this year. Many of those birds weighed in at around 6 lbs processed when they were delivered. I think people were expecting about double that, so there was some grumbling.
Maybe a 4-5 lb heritage breed chicken isn't so bad?
I think my one batch of Cornish Crosses weighed between 5 & 8 lbs processed (at 7 weeks). Of course the Cornish X have huge breasts, which looks a little different than Tom's photos.