Nice butti. I never tried to sex them. I just checked one of my books, "The Manual Of Tank Busters" by Gina Sanford and Richaard Crow. It didn't give any sexing info other than, "Unfortunately, there is no way of distinguishing males from females, either by colour, build or fin development."
Another quote from the book said, "This is probably one of the most belligerent African cichlids." I imagine you already knew that though. It seems to me one of my fish magazines has an article on breeding buttis, if I can find it I'll see if there is any sexing info in it.