Question about adding Blue Tang, possibly Powder Blue Tang

I posted just earlier about replacing a clownfish I lost. Currently I
have a 120 gallon fishtank that has a lot of live rock and as well
blue mushrooms. For fish I have one clownfish (I hope to get a second
soon to replace one I lost), a Royal Gramma, a Yellow Tang, and a
Sailfin Tang. My question, I'd like to get a Powder Blue Tang but
from what I have read anywhere they are very aggressive. I would be
interested in a Blue Tang if I don't get a Powder Blue Tang. They
don't have the yellow stripe but are still very nice and seem more
tame. Would either of these be a possibilty in my tank. One thing
I'm reading about is that it's important it's not the same shape as
other tangs and the two I have are discus shape and even between those
two I've never had issues. This has been a very stable fishtank for
around 4 years.