If you are serious, tank size has a lot more to do with growth. My friend is fanatical about fish and has a house full of various tanks. He bought a few of the same kind (don't ask me what kind, I havn't got a clue) and put half of them in one of his tanks and half in his nephews little bowl that he bought him as a starter. A few years later and the ones he has are honestly about 20 times as big. He told me it is due to them being in such a large tank.