I say save the down for sleeping. I've never worn down on the bike. I've never spent much on brand names either. Just a couple of heavier synthetic jerseys as a mid layer.
Experience may be more important than the gear. If you wet everything out on a sweaty climb while wearing a raincoat, you'll freeze later no matter how much you spent on it. Knowing what to keep dry and how to keep it dry is hard. It's also hard putting on wet gear in the morning right before the ride, knowing you can warm it up and perhaps dry it off with body heat.
I depend more on doing work to stay warm than on clothing, and I need to support that. Good nutrition, rest, and hydration are important. When I'm not doing work, I can get in the sleeping bag.