I have met GGs that tall or taller. Hell, the other day at the grocery store I saw one as tall as me (6'1"). So it's not outside the realm of female heights. I suspect, but don't know for a fact, that my large belly will help more than hurt, because it helps round out my proportions. And as to small hips and butt, well, I've seen soooo many GGs with those same traits.
As I said, I haven't even tried to pass yet, but the more I read other people's stories and look around me out in public, the more I think it has to be easier than we think it is. Is it possible that our biggest obstacle is ourselves?