I rode few times this year when it was really cold(17F with windchill of 3F) and I was still wet afterwards. Problem is if I don't wear a mid layer, it's too cold because my outer shell is just a shell without any insulation.
Any suggestions on a good mid-layer that breaths well?
How about a couple light mid layers in either merino to tech fibre.
On warm days I wear ice breaker:
150 weight tshirt that is snug
150 weight long sleeve also snug or a long sleeve tech fibre such as burton mid layer.
When cold days I add a 320 weight icebreaker pullover