I'm not really sure, but I have a Clarkii Clown who has grown about 1/4 of an inch it seems, since I got him two months ago.
I just bought a Foxface Tang that is about 3 inches long, but I'm getting a 72 Gallon next month...
I don't think that any Tang should be kept for an extended amount of time in anything less than a 50, though I have a 30.