How much warmer is the Atom SV compared to the Proton Heavyweight?

I'm looking for a warmer jacket than my Proton HW, which I find isn't warm enough below -2°C (30°F) without layering a fleece like the Kyanite.

Is the Atom SV a noticeable step up in warmth?

I plan to use it as a standalone jacket, sometimes over a dress shirt when going to the office, and I'm wondering if the difference is worth it.