Sidis are great but very pricy. I was lucky to get a pair for just under $100 on eBay from a gal who got too small a pair. Not surprising, they do run small. I have those in a 39 and a pair of Lakes in a 39, and there's about a full size difference between the two. I'd say the Sidi 39s are about a ladies 6.5, while my Lake 39s are more like a 7.5. I wear thicker socks with the Lakes and thinner with the Sidis!

I have heard that Sidi half sizes are wider than the full sizes. The full sizes do run fairly narrow, fwiw (like a "B" width).

Good luck!
Emily