I just bought a pair of Sidi shoes and others had told me to add a size. I followed the Sidi sizing guide, which claims to compensate for their shoes being more narrow and it ended up recommending a 47 - which is the same size I had in previous shoes (Lake and Northwave). I think I'm a 46.5 but not a common size to find.

The Sidi's are definitely snugger on the sides, about the same amount of toe room. By loosening up the two velcro toe box straps, they feel fine. I've only done a few rides outside with them, as I usually try to break in new shoes on the indoor trainer over the winter, and no problems on the 30-40 mile rides, feet feel fine.