I was always told to go at least one size up with running shoes as your feet tend to get a bit bigger when hot. The accepted is wisdom is that you should have a thumb's width between your toes and the end of the shoe.
I'm a 5' 10" bloke with size seven wide feet and have difficulties getting shoes to fit.
I know what you mean but I already do this as I have no option, my feet only ever fit half my shoe. Don't know what size they are but I can get them into a size one's.
I've gotta sort soon though as pounding the streets in crappy kids trainers is doing my feet no good.