For those of you working on your own meat crosses- What are you feeding?

I've read that too much protein can cause pullets to start laying too young and possibly damage themselves, but if the goal is to breed for a fast growing bird I would think you have to use a high protein feed. Those of you actively breeding and working towards a goal, how do feed? Do you treat them more like breeders and grow them out on a flock raiser to ensure they mature correctly, or do you load them up with protein and breed from whoever tolerates high protein feed best?

For what it is worth I have svart hona x silkie, svart hona x red ranger, and svart hona x cornish. I feel like the svart hona x red ranger would tolerate high protein pretty well, and maybe the svart hona x cornish too, but probably not the svart hona x silkie. They'll all be together though, so they'll all be getting the same feed.