So many different opinions based on so many different experiences. I've mentioned it before, so often it's simple a matter of the fishes particular level of aggression. I don't mean a species level, but that individual fishes. I've always raved about Pacus being the biggest yet most docile fish that can coexist with cichlids. Now I have 3 that LOVE to terrorize my two young convict parents and eat their fry (babies).
My general rule is if they go together young, grow at similar rates and have
PLENTY OF SPACE, and if it doesn't work, you have another option (i.e. another tank for one of the fish) go ahead and try it. Naturally if your at all unsure (heck, even if you are sure!) watch them close the first couple hours they are together and be sure to inspect each fish closely every few hours (except when your at work of course), leave them quite when you turn the light out but listen for splashing which could denote fighting, ya get what I'm saying.
My big tank is ruled by 3 very docile Oscars. They are the toughest thing in there (strength in numbers) but don't bully anyone. Then... my fourth Oscar... SUPER territorial if he is left alone too long he will leave his hole just to beat up whomever he runs across first. Funny part is, he is slightly smaller than the other Oscars (and doesn't start fights with them either, lol)
Okay, I'm talking too much... Id say try it, watch them REALLY close, and have a back up tank if it doesn't work out. If it does work out... get Oscars for the extra tank (I think everyone needs a couple
)