There are a lot of cichlid "community" options you can go with in a 4' tank, depending on your definition of community. The 75g will give you many more options than a 55g, especially if you're thinking CA/SA cichlids. I'll take community to mean a tank with more than a single species. You could go with malawi mbuna, malawi peacocks, a tang tank with shellies, julies, and calvus/comps. Other options would be a good community of dwarf cichlids, such as rams or apistos, keyholes, or checkerboards, and fill it out with dithers. Rainbow cichlids would be another great option.
I would not do jewels in a "community" tank. They're known for their nasty temperament but you could do a jewel colony in a 75g. As for the mbuna you get at the big box stores, many of those are hybrids, you really need to know what to look for to avoid them.