I think 4' is a good MAX number, but remember........ not all fish grow at the same pace. Some get huge, some dont. I dont think the hybrids have been around long enough to say they ALL get 4'. I bought two at the same time and one grew twice as the fast as the other. Same system, same food. I think you can safely assume 2-1/2-4' is a definate.
JMO of course......
bob