Comfy, but zipper seemed whack...
I bought these and RMA'd them after deciding I wasn't crazy about the zipper and the jersey itself. I purchased the large ones in red. The zipper construction seemed cheap and wasn't solid like I've seen and felt in other products including Castelli.
As for the fit, Im 5'10", 155lbs, 32-33" waist with an arm length of 32/33. They seemed to be a bit long in the arms. I believe they would offer plenty of arm coverage for when you're hammering in the drops. The fleece material inside seems really comfortable and the jersey otherwise felt snug.
Just because I wasn't crazy about it doesn't mean you will be too. I love Castelli products but this one just wasn't for me. Hope this helps.