My experience with SA/CA cichlids leads me to think that there is a lot of luck involved. These fish do appear to me to exhibit individual behavior and most people that keep them would probably agree. The same combination of species, in the same tank, with the same equipment, and the same water conditions will not produce the same result. Some fish are just more aggressive or timid than others. In my opinion the only thing you can really do is keep the fish healthy and experiment until a good balance is acheived. If you find the right combination you can keep alot of fish. If you get one fish with an overly aggressive nature you might not be able to keep anything with it. Last year I picked up a 6" male Texas that was traded in because he was overly aggressive. I've been keeping him for almost 9 months with an oddball variety of cichlids and now he is thriving and is no longer a bully. I think it's just impossible to know until you try.
Naldo