Update:
I just butchered several of the boys and thought I would update this thread on the results of using 22% protein by comparing them to a batch of Delaware boys I had awhile ago that ate lesser protein food.
My initial batch of Delaware cockerels were reared and butchered during warm months. They ate a 19% protein feed during the majority of their lives and had a bunch of 10.5% 3-grain non-gmo scratch added to the feed during the last few weeks before butcher. (I wanted to see if a very low protein feed would give them a little fat.) They had food available 24/7. I also kept them mainly in a hoop coop for the final few weeks since they were pestering the layers and to see if I could 'fatten' them at all. I butchered them at 20 weeks.
The result: The carcasses averaged 3.5lbs with no neck, feet, giblets. (I did not butcher the largest bird as he was my keeper. But he was the largest bird by far). They also had large, robust gizzards with a bit of fat around them. The skin was nice and thick with a bit of fat here and there on the carcass.
The recent Delaware cockerels (only 4 butchered so far) were exactly 21 weeks old at processing and lived most of their lives in the fall/winter months. They ate just about 22% protein or higher for most of their lives with several months getting that same feed fermented. (They did get into the layer's 17% protein though and free ranged daily so they also ate whatever food scraps I left in the garden). They had the 22% food available 24/7. Also, I intentionally butchered the smallest 4 birds.
The result: These carcasses averaged 3.875lb BUT this includes necks where the prior batch had no necks weighed. The gizzards actually seemed a bit small- I am wondering if the fermented feed had a hand in this as the gizzards didn't have to work as hard at grinding up the food. The gizzards had zero fat on them. The skin seemed sort of thin and I could not locate any fat anywhere to speak of. Oddly, these birds had longer bones and bigger frames than the first batch with a lower muscle to frame ratio than the first batch.
Since this isnt an apples to apples comparison it is hard to make any conclusions. (20 week butcher vs 21 week butcher; warm weather rearing vs cold weather rearing; butchering all cockerels vs only butchering smallest cockerels, etc.) It does seem, however, that the cold weather and high protein feed led them to have very little fat, less muscle, and more bone/frame growth than the first batch. For instance, a 3.3lb carcass from the first batch actually looks fairly well rounded for a DP bird and a 4+lb bird from this recent group looks gangly.
Not sure if this helps anyone, but I thought I would put it out there in case it does.