I wear 11.5 AA in a street shoe.
I have 2005 Specialized BG Comp Road Shoe and just got a pair of Sidi Genius 5.
I had to put a thicker insole in my Specialized, but the length was dead on. The US size scale on their website no longer matches the one on the tag inside the shoes.
I really like the Sidi's. They are narrow, especially in the toe box and a little short in length. Maybe a 1/2 US size. BTW, the ratchet strap is adjustable to keep the logo (widest part of the strap) in the center of your foot and to keep the tab from dragging the ground when walking!
I can actually wear a thin cycling sock now!