Here are some photos of my tang clan in QT. I have 2 PBT, a white cheek, a powder brown, and an Achilles. They're all juveniles.
You'll notice my white cheek has a large white area like powder browns often do, and is tiny. At this size they're even more difficult to distinguish but notice the yellow spot under the pectoral fins. This large white spot changes to a small dot as they mature. At 5" I would be surprised if yours still has the juvenile markings, but it is certainly possible. My goldrim is probably 2.5-3". My powder brown is about 4.25 for comparison.
All of these Acanthurus tangs are small, the Achilles is transitioning to adult colors as his tiny orange tear drop is getting larger. My other Achilles is in my angel tank and much more striking and larger. My powder blues can be told apart because one has very light colored eyes the other has nearly black eyes.
Sorry my regal angel, "Goliath" loves to photobomb...
Next to each other, my powder brown and goldrim tangs have an obvious color difference. The goldrim is a slate grayish almost dark blue, the powder brown is well... brown lol
They're all in QT because I played the odds and released fish from QT too soon and infected my display. Almost lost that Achilles..