I would not put the Argentea in the same league as a red devil or midas, I would say the aggression would be between a red devil and a jack dempsey. My Largest male is is quite peaceful except towards his mate when she doesn't want to spawn however with other species he just keeps to himself. The females attempt to be more agressive to other fish in a community. Keep in mind size of the tank may influence how you fish behave.
I had a couple of these beauties their pretty aggressive mostly as they grow they start punking other fish a lot more. Be careful what you stock these guys with.
On their baddest, meanest , grumpiest most PMSing day, they couldnt emulate a red devil on happy pills tenacity. Not even in the same league. They are more conspecific aggressive than anything. Not saying they cant be mean, IME they would but not near the level of a RD.
Biggest one I've ever seen in an aquarium is 14"
mediocre aggressiveness, can be mean and can hold their own but it always depends on the individual fish.