I know that cockers (people who raise roosters for cockfights), feed their birds Gamebird feed intended for pheasants, quail, and whatnot. If that's what cockers use, you know it has to be the best for roos.
My 1st flock consisted of 13 roos and 3 hens. I kept all of the roos for the first year. I feed all my chickens Flockraiser and supplement with oyster shell. I've tried feeding both Flockraiser and Layer for the hens but the hens just eat the roosters food anyway so I gave up. Once in awhile when I can't get any Flockraiser, I'll buy gamebird crumble and mix 10-15% scratch into it. I feed my Dark Cornishes that I plan on taking to the butcher a 50/50 mix of Flockraiser/Gamebird crumb and scratch, It seems to keep a little fat on them even when they spend 10 hours a day running around my yard freeranging.
I hope that helps.