Parkas are typically overkill. The hood won't be useful with a helmet in most cases. Layering is the key. I was riding at 32F just yesterday. I had two thin polypro layers on with a very light biking jersey that I left zipped down and had a very light windproof jacket on..the kind you can compress to the size of your fist. I had bike shorts on with running pants on over them that have windproof front and mesh rear. A few layers of polypro underwear with a windproof front that is very light is all that is needed in your temps. Some insulated boots and gloves are needed and whatever minimal head gear (light balaclava) will top it off. A heavy jacket will leave you sweating in those temps. I'm assuming you are riding "seriously" enough to warm up well. If you are riding slow poke like then you could wear almost any heavy thing....