I would think the reduced volume of plumage, feathers being shorter, would enable faster dumping of heat. The cameflouge value seems limited, otherwise it would look more like that of a hen. Another possible advantage, although to me unlikely, is that eclipse plummage can reduces weight and drag restrictions on flight. Hens of my line do seem stronger fliers than roosters, so rooster might make up part of difference by going into eclipse plummage.