I'm at the other far end of the Bell curve. Only 2 layers up top, ever. A thin long sleeve wicking layer under a Gore Phantom 2.0 windproof jacket, and a base of bib shorts under some Pearl Izumi winter bib pants. This combo was "good" down to 12 F (-11 C) on a New Years Day 2018 century that never got above 25 F. This combo also assumes I'll be consistently riding hard and generating lots of heat. Balaclava, winter gloves with silk liners, chemical hand/toe warmers, thick Defeet socks, and winter shoes also helped me to not freeze to death. Changing a flat wouldn't have been fun.