I'm looking at doing 55 gallon with a convict, firemouth, jewel cichlid and probably Tiger Barbs for ditherfish. I might even throw in something to help eat algae and take care of food on the bottom. I'm thinking that if I do it right, I should be able to pull this off. I'll leave lots of hiding places. I'll get the barbs pretty large and before the cichlids are put in.
JDs would be a good choice and I was thinking about those for my 55 gallon. However, the wife wants more fish in there besides 1 or 2. I've had an Oscar in a 55 gallon and he was 11" mouth to tail. He never had a problem turning around. I also haven't seen that many Oscars get much over 12". I think in a 55 Gallon Oscars typically have more problems with water quality and it causes stunted growth.