User Review: REI Men's Zephyr +15
Price Paid: about $125
I was cold in the REI Zephyr when the temperature dipped to around 35-40 degrees and around 30 degrees (10,000 feet last weekend in August and first weekend in September in Colorado). At 15 degrees F, I'm sure I would be freezing.
(It was fine last year in August in Quebec (near sea level) and in Colorado and Wyoming (5,000 feet) when the nights didn't go below 50 degrees.) In other words, I think the 15 degree rating is unjustifiably low.
Also, while it compresses to a reasonably small size, a "tiny nub" it is not. My friend's down sleeping bag -- packed but uncompressed -- is half its size.