I've seen people say they have shy, peaceful psittacus and others who claim they were total monsters who terrorized everything. Mine is somewhere in between. I'd say he didn't get particularly pushy until he made it over the 8 - 9" range. If I were going to do another setup with a psittacus, I think the two most important factors would be tank size and early socialization.
I don't think anyone understands how big a 12 - 14" cichlid really is until they see it in person. On paper a 150 gallon sounds great, but in reality he makes my 210 gallon look like a small tank. If you want to keep tankmates I'd recommend something at least that large.
The only fish mine really doesn't bother are large Geophagus. He and the pike constantly fight, and he pushes around all my severums. I had to rehome my chocolate cichlid because he was relentless with her. I think geos are really the way to go. I'd recommend small psittacus (I got mine at 1") and raise them up in communities. I initially had mine growing out with peaceful stuff like keyholes and angelfish, then around 5" they got pushy and I upgraded them to tankmates like severums and Mesonauta. Around that time they also became really intolerant of each other, so I kept mine and sent the rest to John (snookn21).