There is a thread on here with a 10"er. It will certainly take a long time to reach any size over 8"+ granted. But they grow fairly quickly. As for aggression it does come down to the individual, as is with any cichlid. But I personally wouldn't mix them with a FM, least of all in a 55.
Salvini, Jack Dempsey, Ellioti, Rainbow cichlids, just to name a few.