I feel ya' on the Acara thing, I looked for one for over a year and finally gave up and ordered a group. I originally wanted a GT for the tank but didn't want to have to deal with the attitude; so I went with the calmer cousin, lol (feel like I made the right choice

). All of mine seem very calm and tend to shy away from fights, when my mating female drops eggs on the other hand, she is a force to be reckoned with.
As far as the flagtail not being with smaller fish; I keep mine with a group of 5 geophagus steindachneri, which are no where close to even their small framed full size (they're only about 3"-4" now). They've been living peacefully together for months with my 8"-9" flagtail. It may be the space or the fish or who knows what but they seem just fine together. I will tell you though he's no push over; he (my flagtail) chases the silver dollars around all the time, more so even than my cichlids.
Good luck on the hunt and make sure to post pics of what you end up with!