@Miss Lydia, I have not heard of that one. I've heard "males have bigger feet" before, but I've never paid enough attention to confirm it though. That's another reason I love my White Sebastopols. As soon as they hatch I can sex them by color/pattern.
3-4 months is a tough age to sex geese accurately. They haven't quite gotten their adult voices yet so vocal sexing will also be hard. Post new pics at around 6 months.