It's not always about the cichlids' size but their temperament. People will argue that large cichlids like oscars can fit into smaller tanks than a 125, but a 125 gives you a 6' footprint which allows them more room to get away from each other. It allows them a little more breathing room, so to speak. This is why a 6' tank is preferable over a 4' tank. Do yourself a favor and look for a tank on Craigslist that's at least 6' long if you want to have a handful of larger cichlids. Add some driftwood or big rocks to break up the line of sight and you should be fine.