Well, the need for a warm jacket is here. This past week we've been having highs of 10 degrees Celsius (50 F) and lows of 0 degrees Celsius (32 F). Rick had mentioned the heat island effect. That probably explains why it never gets below freezing. On the rare occasion that it does snow, it doesn't stay around for long.
I went around town and tried on some jackets, all sized 'M':
OR Trancendent Hoody
Rab Microlight Jacket
Patagonia Nano Puff
Patagonia Micro Puff
MB Thermawrap Parka
MB UL Light Alpine Down Parka
MB UL Down Guide Parka
The fits for all of these items varied. But before I get into that, I wanted to run something by everyone. My understanding is that for best heat retention, it is best for the layer item to fit snugly, not in a constrictive sort of way, but in a way where the item is in contact with the body. With some jackets the torso is very big, so I have a very large air pocket around my body. This pocket of air tends to chill me. However, whenever I put on a jacket with better (more snug) fit in the body, the air pocket is reduced or elminated and I feel warmer.
If that's the way puffy layers are meant to be warm, then the MB UL Down Guide Parka seems to fit the bill (it fits me snugly without being constrictive). The only thing is that the sleeves come up a bit too short. I will either have to just learn to deal with it or get creative.
Other likely candidates include the OR Trancendent Hoody, as well as the Rab Microlight jacket (I prefer a hoody though, but the shop didn't have any).
I did try on the Arcteryx Atom SV, but strangely it was a bit large in the torso area. I already have the thinner version, the LT, and I don't recall it fitting me so loosely. Perhaps I need to go back and try it on again. I did do all of this running around and trying things on on Christmas Eve, and with the shops crowded and all, I wanted to get the heck out of there the moment I entered.
I did think of another use for the jacket--something I can use for breaks on snowshoe/cross country (ski) trips. I'd keep it in my pack and pull it out whenever I stop. So, with that in mind weight is now a concern.
Thanks for everyone's input. Much appreciated.