Here is an article written by
@4FordFamily that covers the topic in general (and specific comments about Acanthurus tangs).
I should preface this by saying that Acanthurus tangs specifically tend to be very fragile with regard to dealing with Ich/Velvet etc. If you're not quarantining or planning to quarantine I really think you should avoid pursuing these tangs specifically.
With all of that being said, my tank is overstocked with tangs including a Goldrim (Acanthurus nigricans). When I introduced it into my hierarchy it was half the size of the larger/more established tangs. My white tailed bristletooth tang is the smallest tang in my tank but it is also the aggressor and boss interestingly enough.
All of that being said, my Goldrim was introduced last and it has outgrown the other tangs 2:1 and is close to being the largest after only a year.