In terms of aggression the Robertsoni easily dominates the tank, but dosen't really do any damage. Ive heard conspecific aggression is very high though.
His tank mates are a 7" female Rivulatus, 3" Male Convict and a 4" Pearl Horfseface in a 6x18x18. I would say the Horseface will grow to be the most aggressive, the Rivulatus is pretty tame. Im soon to add a 5" firemouth and maybe a few Cons from another tank so things might change.