A true midas would be pretty aggressive, as Far as I have heard on the site true Labiatus devils tend to be more relaxed than true citrinellus midas, so the true midas would be as aggressive as say a store midevil.
The aggression level of any amphilophus (pure or not) will be based on the individual temperament of the fish.
Anyone that attempts to tell you otherwise hasn't kept enough to know what they are talking about.