It is not as simple a question to answer as your other answerers have suggested. The reason is that the thickness of a lens is related to more than index of refraction. As you are aware, the index of refraction affects lens thickness. The higher the number the less material is needed to create the same power. Therefore, a higher index of refraction will allow the optician to make the lenses thinner. BUT, minimum center thickness (this is controlled by governement standards) also plays a role in overall lens thickness. Polycarbonate is not only a higher index lens but it also is extremely impact resistant. Therefore, the government will allow a polycarbonate lens to be cut to a significantly thinner center thickness. This allows a polycarbonate lens sometimes to be cut thinner than other high index lenses that cannot be cut to an extremely thin center thickness. The overall thickness will also be dictated by the size of your frame. If you choose a very small eye size frame then there may not be nearly as much difference in overall edge thickness between two relatively similar indexes of refraction. The larger the frame, though, the more apparent the differences may become.
Me. I am an optometric physician.