They are all young. toughly an inch and a half each. I'v had them in the tank together for about 3 hours now, and the only fighting going on is between 2 JD's. They are fighting over a hiding spot. I broke them up because they wouldn't stop, and now both of them have scaled missing on the tops of their backs from the rock they were fighting under.
I have a 7" jd male and a 6" gt male. Got them when they were about 2" and they do great together. The jd hides most of the time and the gt roams the tank and eats alot more. They never fight with each other and never have. Most of the fighting in my tank is between my 5" red devil and 5" clown loach.
My female green terror was going after my female jd so bad that I had to give her to my buddy (the jd that is).
And speaking of my green terror, my midavil is probably 2 to 3 inches taller than her and an inch or two longer and yesterday I saw her trying to intimidate the midavil. After my midavil got over her disbelief she promptly chased her off and reminded her who queen of the tank is.
Bottom line, cichlids are cichlids, their temperments vary. Use their reputations as a guide towards their aggression but there are many different factors that determine whether 2 particular ones are a good match.
I have found that green terrors in general seem aggressive while jack dempseys seem to be tough but defensive.
definitely a hit or miss with these guys. i have them in my 210g. both are about 4~5" and i have never seen one chase the other. they are both males BTW...