I used to wear a Carhart shirt as an outer layer. I never realized how freakin' heavy it was until I got a $23 Performance C9 jacket from Target. It allows pit, side, and arm venting.
Down to 20 degrees I wear the C9 jacket, 100% wool sweater from the Goodwill store, and a wicking T.
The vent areas on the jacket are wet to the touch after my rides but I stay warm and comfy. The jacket zipper allows adequate regulation. I am an extremely heavily sweating person.