Some places you take a measurement of your feet and send it to the company so they know how many inches which then transfers into a size they carry.
why don't you just measure your feet?
You should come to the Netherlands. Many Dutch women have big feet and stores actually sell for those with big feet. I've seen size eleven for women in shoe stores. You'll be able to wear heels which are your size rather than only wearing men's shoes. Imagine that!
But where are the shoes from. If it is an Italian make I would suggest you go for the eleven. But if it is American try the ten and a half.
If you are a typical woman, I doesn't matter what size they are....You simply have to have them! LOL
I'd get the 10.5 ,and be prepared to send them back for 11 if they are too small. From what you said 10.5 is your Usual,and is best chance of fitting. :)