I think they are as cold tolerant as anything out there without much fat-they are a lean breed, not fatty, so, they are not going to have the fattiness to protect them, but, I would imagine they could take that kind of cold, so long as you keep them out of the wind, and give them enough roost to cover their toes. We have only ever had -25 or -30 here once in my life, we had RIR's and Jap bantams then, all their combs and wattles froze off, and they lost some toes, but, they all lived. The Cubas don't have the combs and wattles to freeze in the first place. You have games or game bantams yes? They are a match for those if not better in cold tolerance.