To a Tang, a 90 is not much bigger than a 75 or a 55 as they are only 4' long. The best Tang I ever kept in my 75 was a Tomini Tang. Unless you want to swap out when the grow, there aren't many at all that would be happy in a 4' once full grown. Maybe a Kole or Scopas?
Those are not the best suited for your size of a tank. They will do ok in a tank that size, but then again, people can live in prison cells and closets for a long time, as well. If you absolutely must have a tang, I suggest Ctenochaetus species of tangs, since they are the smallest in the family, in general. The aforementioned tomini tang is one such fish, though they are a bit more difficult than other species.