Shoe size comparison

Does anyone know how Scott shoes compare in size to Sidis? I have a pair of Sidi's that are 39.5 and fit great. My 39's are too snug for really long rides, and the 40's are good for winter with extra socks.

I'm looking at a pair of Scott shoes, not available locally. They only come in whole sizes, so wondering if I should do with 39 or 40. Does anyone know how they run?

What's the return policy? If possible, buy two sizes and return the other. I think sizing cycling shoes is as crazy as trying to size bikes - every company has a different fit.