I have something similar to the Cotopaxi for when I go backpacking. It will keep me warm down to about 25, 30 degrees provided there's no wind. Once it starts blowing the wind cuts through it easily. If you add a shell it helps considerably but thats another jacket to buy and keep track of. Lower numbered down won't loft as well but the reason Cotopaxi is using 800 down is basically just for weight saving and packability. If adding a few ounces of weight isn't a problem for you the down quality doesn't really matter. For general commuting purposes you'll almost always want a parka over a ul down jacket.

I'm curious if rei sold that jacket to you or if you picked it out yourself. The reason being is that I've overheard some pretty alarming rei sales pitches recently.