Somehow I lucked out and ended up with all male severums in my 150. There's been no fighting or displaying as a result of trying to "get the girl," so apart from the occasional tussle for dominance (usually during feeding) I've had a mellow group.
I do have one female in my fish room, in a 55 gallon, and I'm afraid to ever introduce her to the 150. I'm afraid if I introduce any females, all hell is going to break loose and things will never be the same.