Well that all depends on how big of a snake you think you can handle. A BCI typically doesnt get much longer than 9 feet depending on sex ( females being typically larger ). Afrocks, on the other hand, have the potential to get over 20 ft and over 200lbs and generally have a much nastier disposition. BCI's have a much nicer disposition and dont require such a big enclosure.

As far as two snakes living together, its a bad idea in my opinion. You have no way of telling which snake poo'd, if you get two males in the same cage you can have fighting and potential death, and if you have a male and a female you can end up with unwanted babies. My rule of thumb is .. two snakes = two enclosures. You dont have to worry about sharing potential diseases, and competition over food/living space with two seperate enclosures.