Well lets deep dive your options/desires.
You want a solid color. Is white a consideration? You seem to be aiming toward a good meat bird. So white would be a great option if you, or those eating your birds, find pin feathers unsightly. If you don't care about pin feathers in the skin, pretty much everything is going to come in a (mostly) solid color. Is there a reason you wish for solid color? White is a consideration. My preference would be black or buff though. Solid color would be nice just since that's one less thing to have to worry about when deciding who is SQ/BQ and who is a cull. I already have my light Brahmas and need to hatch more of them in order to get a bird with good type AND color. Solid colored breeds really only need to worry about type so less chicks need to be hatched to get a quality bird.
Have you considered slaughtering before 6 months? Birds can be pretty tough by 4 months of age. Birds can also be, depending on your roasting pan, too big at 7+lbs. The sooner the better is how I'm looking at it. I just want them to put meat on instead of just a big meatless frame.
How cold does it get during a typical Winter? Generally Summer time is when casualty and stress occur, not Winter. Is your Summer time harsh? What sort of humidity do you see on a typical day in each season? Winter is usually never in the negatives. I would say teens and the twenties is the most common. Summer rarely goes in the 90's. Not sure about humidity.
Are these birds being kept in confinement or ranged? This might have a great deal of impact on feed conversion and weight gain. Well the breeder birds will mainly be confined but will get time out in the run. All of the birds I'm raising up will get to free range.
And as for the New year 50+ Buckeyes and 8 La Flèche to bring in the New Year. ABA Leg Bands on the way. Ready to start culling the three week olds(ITS NEVER TOO EARLY).