Three comments:

As mentioned above, continuous baffles are a great feature because they give you a degree of flexibility.

When choosing a bag I prefer to compare the amount of loft instead of temp ratings. It's a much more objective comparison. Temp. ratings can be all over the board and some manufacturers make some pretty wild claims.

Lately I have adopted a two bag system. A summer/fall weight bage inside an overbag. Not the lightest solution but cheaper and more flexible than buying a dedicated winter bag.
If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.