I personally wouldn't do either for any period of time, except as a grow out system. I assume you expect to have them for awhile and so both should grow, in which case they will outgrow a 4' tank. They are also both sensitive fish (prone to disease and parasites) with similar body shapes. Could be trouble, IMO. I wouldn't recommend it. Maybe one or the other for the short term..and assuming you have a larger system somewhere...but otherwise I wouldn't recommend it.