One thing I've noticed with hatchery stock. If you get 15 to 20 cockerels of the same breed from a hatchery (I have) there will be a big difference in the best and the worst. I haven't tried breeder stock when they are breeding for size (I have for other reasons) but you will see some difference in them too. If you do go for a specific breed, don't just get one or two. Get a few so you can select the best to breed and eat the others. Even the rejects from a breeder's flock will probably be better than the best from a hatchery as long as that breeder is breeding for size and they know what they are doing.
*nods*
I had 5 Blue Australorp cockerels to choose from.
1 was awful -- skinny, gawky, and not built like an Australorp at all.
2 were ordinary -- looking about like you'd expect from a hatchery Australorp.
1 was fairly decent --the biggest of the bunch with OK coloring and reasonable conformation.
1 was superior (see my avatar) -- big, wide, as close to proper conformation as a hatchery bird is ever likely to get, and with better coloring and lacing than the birds in the hatchery catalog photos.