I've found regani to be very aggressive in anything as small as a 150 gal tank, after I gave it away, it killed a much larger red devil, some carpintus and a couple jags.
Herichthys (xCichlasoma) bocourti and pearsei(not Vieja's) seem very mellow, but get very large, mine grew to over 15", so in the end, a very large tank would be needed.
I have also kept fenestratus, zonatus, bifas, argentea and maculicauda, and found them all to get aggressive in anything as small as a 150 at some point in their development.
The least aggressive Vieja for me has been breidhori, even when they spawned in a cichlid community,
there were no deaths.
I've found their aggression to be more bluff than bite.