I'm a huge fan of knickers. I have owned several pair from several different companies. When my go-to pair for 40-50 degrees, finally wore out, I was on the hunt for a new pair.
I was looking at these and the Giordana FR-C Pro and was told by CS that the Castelli should be warmer. I bought both and while I loved the fit and pad of the Giordana, I could tell they were not going to be as warm.
I'm 5'9" and 160lbs and got a Medium.
The fit is very good. The length goes to just below my calf, which is what a proper knicker should do. They are warm and windproof in the right areas. I rode these on a really foggy day and I was getting moisture build up on the outside of the legs, but stayed dry. The straps are excellent. The fabrics are excellent quality. I never felt clammy.
The bummer is the pad. While Castelli calls it their top of the line, I prefer the KISS AIR 2 pad. The Progetto X2 pad in these, is not as comfortable. It kinda just flattens out and you feel your seat more. It also feels a little forward and I have to pull the tights from the back occasionally. I know Castelli designs some of their clothing to be race fit and thus worn in a more aggressive, bent over position, so maybe that's what's going on here.
I have the Nano Tutto Nano kinckers and while they are not as warm, the KISS AIR 2 pad is much more comfortable.
Over all these are a great knicker for Mid-weight warmth. Fit great, but the pad keeps these from being excellent for me.