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Have you tried the wind block jersey?
https://www.rapha.cc/gb/en/shop/classic-winter-windblock-jersey/product/WJY10XX
I wouldn't tend to ride in much below zero due to ice, but I would typically ride all year and on the coldest days, that with arm warmers and thick baselayer vest I got from Aldi underneath, and brevet insulated gilet on top is all I've needed all the way up to long threshold efforts before starting to get hot.
I get so much wear out of it in autumn/winter. I was out on Weds morning for an hour when it was around 2 degrees for a tempo/threshold ride and wore all the above without the gilet and it was just right.
Last night was the first ride in a while where my Brevet Insulated Jacket just wasn't warm enough (was about 2ºC according to Wahoo). I had a long sleeve jersey and a mesh base layer underneath and a snood around my neck to stop warm air escaping, but really felt the cold particularly on my arms and chest. Was just about bearable on the flat but coming down Highgate Hill and Holloway Road was miserable
Would something like the new PT Winter Jacket be warmer, or do I need to look into thicker base/mid layers?