That's comforting, I've heard a lot of people say the Ultra 20 didn't go down to 20 very well. I'm thinking of getting an Exped Downmat or that IAC before I take any bag down to 20. And if the new quilt is warmer from the extra fill, well, that's all to the better. :)
I'm only 5'9", but do you think there's any point getting a size large, so it covers more of the head and has extra width to wrap around? It's "only" 3 oz heavier.