They don't have to end up so heavy they can barely walk, so you could try the CX without worrying about that. It really depends on what you feed and how much if they grow that fast. If you are in no hurry, you can slow their weight gain down and thus increase their mobility and health status. For simply pounds of meat for the freezer, they are and will be the biggest meat producer breed you can grow and they get there in the shortest time~even on slow down.