I can't seem to decide on which tank to get for my fancy goldfish. A 40 breeder would fit into the space I want to put it more comfortably, but a 55 will fit as well. Also, the 40 breeder seems to offer a bit more side to side swimming room and surface area. If I go with the 40 I'll probably only get 3 fancies total, but with the 55 I'd get 4. Also, I have a 55 and it's a bit skinny. I thought the fish might appreciate the extra depth. What do you guys think?