Compared to it, the Frobisher is a bargain. It has, as you note, about 16 ounces of down, versus 21 for the Rock & Ice, and doesn't have some of the bells and whistles such as the powder skirt. But it has a Dryloft shell, a long, roomy cut, and good-quality 700-fill down. And it's only $286 U.S., which means it's very difficult to go far wrong. As far as a "decent down jacket" goes, it's a winner- the Rock & Ice is simply overkill.
Mountain Hardwear's Sub Zero SL Parka ($295) is similar to the Frobisher, but uses 650-fill down (slight difference) and Mountain Hardwear's proprietary Conduit outer fabric, which is more waterproof than Dryloft.
So that's a tough choice between the Frobisher and the Sub Zero. Ideally you'd find a store that sells both to look at them side by side to get a sense of their respective construction quality, but that could be tough.