Severums, uaru, and green terrors would be a pretty cool tank, I think. What about a Geophagus species in that mix? I have seen GT and Jags together, but it was a 600 gallon tank. Side note; As a fly fisher, when I see “GT,” I always think it means Giant Trevally!You would be better off keeping fish like severums, uaru, crenicichla, guianacara, etc (less aggressive SA cichlids) with the green terror. That would make quite a display in a 300 gallon with some chalceus and silver dollars.
Side topic note; Female Apistogramma can be vicious during spawning. I was shocked when I saw it for the first time. Like a bright yellow 2 inch fishy blender of death, rag-dolling males six times their size. Pardon my digression.I agree, females can sometimes be worse than males.