I just went through this. I just bought my second Big Agnus bag (guess I am a big fan) with the REI coupon and dividend. I went with the Yuma (40 deg down) to go with my Crystal (30 deg). I do more backpacking and the Yuma will save me space and weight in the backpack during the summer months. The two can be combined together for a 10 deg bag. For me I need to add 10 deg to the actuall bag rating, i.e. a 40 deg bag is really a 50 deg bag.