Caz - I meant a single Jade eye or Rainbow cichlid in a 10 gallon not a pair. I wouldn't go with anything less than a 20 long for either fish (convicts, too, again one in a 10 or 2 in a 20 long).
Carpinte is the species of Texas I had. He was great. Jumped from 1 to about 5 inches in somewhere around 5 months, then grew another 2 inches the rest of his life. Some get bigger, actually, there is a very good chance he was a she...but since I only had the one I never took the time to figure it out (which is strange since she/he lived a decade with me). I do know some stay smaller than the books list.
A 55 is a very nice size tank, but it's a real bear to move. I moved my tank back on forth from my dorm during the breaks, so back then I only kept a 20 gallon high. I kept a parade of cichlids (single specimen) in the tank. I'd buy babies, raise them until they were getting to large for the tank, then trade them in for another baby and some supplies...it kept me in fish for 4 years. If I were to do it over again, I'd go for the 20 long or 29 with convicts, jade eyes or rainbows with 3 small dither variatus platys. That way, you get more natural behavior, you'll probably get breeding behavior, plus if you can get a nice pair (which is what makes convicts great - they're so easy to sex and they pair up easily) you may get some fry surviving to trade in size for supplies...