I've worn my felted wool 'pea coat' style coat in everything from -15F to 40F. The collar flips up and protects my chin and neck when it's really cold. When it's warmer, I'll wear it unzipped. I've worn in through snow, sleet, and light drizzles and it's always kept me warm, though I have treated it with a mix of tech wash/waterproofer and lanolin, so it's pretty darn water resistant. I toss a $4 neon and reflective vest over it, since it's dark grey. Without the vest, I'd be much less visible, and if I ever got hit, you know it'd be my fault since I was wearing subdued colors...
Plus, it's a training ride, so a bulky coat that catches more air is a good thing. Making a training ride easier by focusing on 'aero', especially when the roads are less than optimal and possibly iced is just plain silly. If it gets really cold, I'll put on a wool sweater and when it's below 0F, I'll sometimes toss a 3XL wind shell I picked up at Marshalls for like $12 over top, to keep the wind off. Above 0F I like the wind on the coat. It blows through the coat, somehow keeping my sweat to a minimum while not making me cold. I'm guessing the incredible breathability keeping the sweat down probably contributes to the long-term warmth my coat seems to provide. It's much much better than my technical stuff, like my extreme cold gear from underarmor, which gets wet and cold after an hour or so.