It's interesting to be able to tell early, but truth be told, it doesn't matter much. I will grow them out, and keep a record of their traits. Yesterday I made DH, and my doctor very angry at me. Later on, DH was looking at the chicks, and he was feeling all warm, and fuzzy. He asked me what I would do if they turned out to be roosters. I replied that if they were not prize winning quality, they would taste good. DH almost fainted. Moving into the dog house now.......I had a list of wing feather sex able breeds but the link does not work. I will check on some University sites today and find a new list.
I did find a note that a hatchery spent three years in the 50 coming up with a line of meat birds that were feather sex able.