I'm really not sure how fast they grow to tell you the truth. I've just seen them get very large and the thought of a naso in such a small tank gave me the "willies".
Believe me, all it takes is one sick fish added to an established tank that kills others and is VERY hard to catch and treat with all the rocks in there to make you wish you employed QTing new arrivals. Others can profess to some degree of luck only when they say they've fully stocked a tank and had no ick or marine velvet, or other cummunicable disease break out.
"Life may not be the party we hoped for but while we are here we might as well dance!"