(Let me put on my armor as I prepare for the attacks by the tang police).
I bought my sailfin when I had a 240 gallon tank. He lived in there for 3 years or so, and didn't grow noticeably. When I downsized to my 90, I kept him for another 3 years until I took down my tank and found him a new home over the summer.
In the 6 years I had that fish, I don't think it ever grew. And the 240 it was in should have been big enough for it to grow if it was going to grow. The sailfin was much smaller than my yellow tang and even my foxface.
So would I put one long-term in a 90? Nope. Would I recommend anyone get one for a 90 that doesn't have plans to get a bigger tank or re-home it? Nope. I really think they need 6 feet of swimming room.
I did it and my fish was fine, but that doesn't mean other people would have the same results.