I've heard we will have some color options in the future on the SG coat.
I agree the two jackets in question are really different classes. The SG jacket is most similar to the KUIU Super Down Pro. The Pro has 5 oz. of 850 fill. The SG is 5.3 oz of 850. The Pro weighs 13.4 oz, the SG weighs 11.8. The Pro has a more durable shell.
The Sitka Kelvin WS is a better comparison to the Chamberlain. The Chamberlain is one of the warmer puffy's I've tried followed by the Sitka Kelvin WS. And with good reason, they are the one's with the most fill. With more fill, you're going to get a heavier jacket. That's why the KUIU Ultra SD weights in at 7 oz. It only has 2.3 oz of fill. (and a super lightweight shell), while the Chamberlain and Sitka WS are North of 25 oz.
I've owned/tested about every hunting puffy made. I use several different ones depending on the climate I'm going to be in and how "packable" I need to be. For all out protection against the worst elements, I like the Sitka Kelvin WS.
For early season sheep it is tough to beat the KUIU Ultra's but this year I'm checking out the First Lite Brooks. For a damp climate such as Kodiak, I like the Kelvin Lite, Regular Kelvin, the WS or the Kifaru Lost Parka.
If I could only own TWO puffy's, (one for early season, one for late) they would be the FL Brooks and the Sitka Kelvin WS.