Your mileage may vary, but with a tank that size, and having the Bangaii already established I'd probably avoid it. We added two Bangaiis in our 65 gallon and the resident Bangaii got very aggressive so he got moved to the in-tank hospital tank (solitary confinement, anyone?) and later down to the sump. Jack first started chasing the other Bangaiis and then he proceeded to get nippy and aggressive with our other fish as well.
Best wishes, what ever you choose!