I no longer have either of them. I picked up a lot of similar fish besides these two. My Argentea was not the dominant fish in the tank. He was however far too aggressive, randomly. It would be chilled out one moment and then hit a fish extremely hard out of no where and split their fins apart, and knock a lot of scales off. Basically, mine was an assassin. He wasn't with me for too long, only a few months. The Synspillum WAS the dominant fish in the tank for a very long time. Very aggressive, very assertive until the Bifasciatus I got outgrew her considerably. I sold her about 2-3 months ago in a mass exodus of all my female cichlids. I had some breeding/courting aggression that was just too much for my tastes. I only have males left now: Regani, Bifasciatus, and Midas in a 450g tank with loaches, and other bottom dwellers.
I hope that answers your question.