HOW MANY IS TOO MANY IN A 40 GALLON TANK

I have a 40 gallon tank that is home to my South American Cichlids. I have not been able to find much information on them. I've been told they are more aggressive than their African counter parts. That is definitely not the case in my experience.

In my 40 gallon tank I have:

                                             - 3 Parrot Fish

                                             - 2 Black Convicts

                                             - 2 Angels

                                             - 2 Fire Mouths

                                             - 1 Tiger Oscar

                                             - 1 Albino Oscar

                                             - 1 Pleco

                                             - 1 Bristle Nose CatFish

From what I have found online, my tank is over-stocked as they will fight for territories and be very aggressive. As I said, in my tank that is not the case at all. My South American Cichlids are doing awesome. They are not aggressive towards each other at all. If anything my big Black Convict sometimes lunges at the smaller one but doesn't even bother giving chase. They are more interested in me when I watch them and eating. 

I watch them closely so in the event that they become aggressive I have empty tanks I can move them to. Eventually they will be relocated into my 60 gallon tank but as yet it's not set up. I had it given to me so now my hubby just has to build me a cabinet to house it in. Hopefully they will be moved in the near future.