Mary,
The Down Sweater here is warmer than the Ultralight Down Sweater. The Ultralight is a tad longer in the body, but no enough that it would make a big difference in the weight of the garment.

I found the Down Sweater to be warmer than the Ultralight. I'm not sure, but I think it's because the Down Sweater fabric is more windproof and it has a higher chin to block out the wind. According to the Patagonia rep, the Down Sweater has 85g of down and the Ultralight 80g, so in theory, it should be pretty comparable. But standing outside in each, the Down Sweater was definitely warmer.

Also, the Ultralight is about 1-2 inches longer than the Down Sweater and is a little more fitted. I like the length and looks of the Ultralight better, but unfortunately, the Down Sweater is warmer.

The down sweater has far more loft...poofiness....air. It is warmer!