I would see no reason it wouldn't attain that size, other than from stunting, disease, etc. from being in a small tank.homer3d455840 said:However it would most likely take a clown loach over 10 years to grow to this size...if it ever attained it.
NTT, if you really like the clowns, why not go for the kuhlis, but do 6 or so? They are simmilar in color, still a loach, and do not get too big. Then you could take your pick of the rams(my choice) or guaramies(good too).
The problem with trying to keep the clowns has been stated, sometimes you run into financial problems and cannot afford the larger tank. Also loaches like to school, and you will definatly not have a tank big enough for ..6?.. of them even with the 55. I would plan your stocking arround your current tank, and if and when you do get the 55, plan the stocking for it while it is cycling.