So what I own is a Montbell Alpine Light Parka, and a Patagonia Down Sweater.
The reason for buying two is that I'd have places like Chicago which does cold I could never describe, to places like New York which over a 5 day period would vary between very cold and above-freezing rain. My Montbell Alpine Light Parka, if I'm walking more than about 10mins, it has to be a max of -10C /14F for me to not overheat. If I'd gone for anything thicker I would not move without sweating above 0F. However, down when you put it on is not initially warm, it has to build up some heat from the wearer so for the first 10mins it can be quite chilly. That's the downside, what do when its not "Canada cold" ?
For temps about or just below freezing the Montbell is too warm so then I have the thinner and more ubiquitious on sale Patagonia.
For more stationary or very cold I then wear BOTH, I got the Pata in medium and the Montbell in Large and I put the Montbell on the outside. That is then what I'd call "Canada cold" but at least you bought two items which in combination will see you through more conditions, if you bought one thick Parka you'd solve one problem but then still need to buy something again not as warm and end up spending more.
The Montbell packs to 3L, the Pata packs to 2L so carrying both and packing what I don't need needs 0L/2L/3L/5L stored space.
I travel across USA widely, last week I went as south as Panama City, Panama. My luggage is 40L, and I brought the Patagonia as I was only passing through Houston, TX. If I were passing through Chicago I'd pack the Montbell. As it turned out, I was in an exit row seat near the the exit (first off the flight through immigration) but I had to wear my Patagonia zipped around my legs as there was an icy blast coming through the door, and then a windproof on my torso.
Montbell is cracking good value and quality, but is harder this year to get the value, I paid $140 for my Alpine Light Parka in Nov '10 and I paid $100 for my Patagonia but it took patience to not get it in 'orible orange.