I'd go for a very breathable jacket that goes to around zero (probably with good thermal underwear underneath. When it get still colder, pull a nylon (or equiv) windbreaker over that you can take off mid-ride as you warm up.
For me, the secret is to be warm enough the first 5 miles or so, then be able to shed layers to keep sweat down. Failure to do the first can mean (again, for me) a ride where I never do warm up and cannot get to a good, heat generating speed and effort.
Good hats under the helmet are another approach that are easily taken off as one warms. (At -20F, perhaps the hat under for the whole ride and a windproof shell over the helmet for the first miles.)