Mire, wish I could help you with your question. I've only been raising birds a year now. I'm raising to eat so
I can say the first breed I had was Barred Rock cockerels from ideal hatchery. I liked their growth rate at 18-20 weeks they dressed out well. I don't know the weights. Keep in mind that hatchery stock BR's are not true barred rocks and are a mix of what breeds I don't know.
The Bielefelders I have now have really won my heart. They're temperaments are awesome but from my observation they don't grow fast enough for me to make a good dual purpose meat bird. I don't see myself butchering them to eat because I've become to attached so I have a predicament when it comes to keeping them. If someone had children they would be great around them. Of course there's always a bad apple in the bunch. I have the Barbezieux going also. In a few months I'll cull a few and report on taste and sizes. If what they say is true it should be the best tasting bird I've ever had.