A lot depends on your goals and management style. I'm not familiar with the grey rangers--but I assume they are a slower growing bird, expected to be harvested 10-12 weeks? As for the CX, they'll gorge if you let them have free choice. When I raise CX, they move every day and I give them feed twice a day based upon what they can consume in 30-45 minutes. With that approach I have a 3% mortality rate compared to 10% when giving greater quantities of feed. I also put feed and water as far apart as possible to encourage them to move around. And I'll give them treats twice a day, again to encourage them to run around their shelter. The Grey's are likely more active and will also encourage the cx to move about.
I'll be the first to admit I have not gotten to my target conversion rate yet--but getting closer. In a perfect world, with perfect grass and perfect bugs, you should get 1lbs of carcass weight per 2lbs of feed. I'm running about 3.6 on my last batch with an average carcass weight of just over 6lbs. A couple went as high as 8lbs.
