It's warming back up this week, been in the 90's with nights in the 70's, and August is usually MUCH hotter than this!
I was reading a translation of the Marans Club of France site, and I believe the size guidelines it gave were up to 9 lbs. for a cock and up to 7 lbs. for a hen...but of course I could have that totally wrong. I was surprised to read that, though, because my hatchery cuckoos are noticeably heavier/larger than both my White Rock and Buff Orpingtons of the same age.
I'll be interested to see how much size these coppered black fellows get, and yeah, I'd imagine our birds are pretty well related.
We did notice that our first batch of chicks, that we kept in the basement brooder for 4 weeks, feathered out much more quickly than did our next two batches, which we put outside at 2 weeks old. So maybe that has something to do with it.