well its kind of hard to figure that out right now... i think id like something a bit more different or 'rare' sort to speak i just cant find anything uncommon that will fit in a 55
i like myrnae alot
cross argentea off your list they need a 125+
i would do a small Ca specie tank
try some cutteri, myrnae and what ever else you can get your hands on most of the ones you listed arent readily available in the hobby
salvini are good. if you want something different as said above paratilapia polleni.
do you want a single larger pet fish or a comunity or breeding pair?
have you checked out juwel cichlids? ive bred those in a comunity of sa/ca cichlids.
they are a riverine African species but in all experience ive seen work perfectly with new world cichlids
im looking for a community that can be kept in a 55 gallon for a while until i deiced what im going to breed im thinking ill breed Herichthys labridens ,Paratilapia polleni