I don't have the castelli but the rapha pro team jacket is very nice. I wear it down to low 40s fine. It's very tight fitting which is good for fit but bad to out on base layers under it. I ride it with a short sleeve rapha merino. Adding a long sleeve merino is not possible in the arm section for me. Once again though, very nice jacket

Just to throw a spanned into the works I was out today in my Rapha Wind Jacket, temp. was 8 celcius/47F. Underneath I had a short sleeve jersey and two lycra type baselayers, could have done with one. Too warm. Ride length was 4h. I really like the jacket and you can wear it pretty much whatever the temp. Summer rain its great over just a short sleeve jersey.

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--Max.

Yeah, the wind jacket is windproof but not warm when worn alone. You have to figure out what to wear underneath it. At 8oC I wear a merino base and the Rapha winter longsleeve jersey. 8oc isn't cold, - 8oC is.