Hmm - I wear a 38 1/2 or 39 sidi road shoe/mountain bike shoe and I wear a size 7 usa women's shoe size - but I have a rather narrow foot so maybe that makes it more to size for me. I have a 38 specialized road shoe that has more room in the toe than my 39 sidis.

You don't need as much room for your toes as a regular walking shoe , i.e. a thumb width from toe to front of shoe, but you should have a little room there; especially if you are going to run in the shoes, i.e for cyclocross.

jan