I bought these after reading the reviews, after talking to the manufacturer and after a LOT of experience with other gloves. I'm a ski patroller and I get a lot of outside experience in subzero temps when I can't go inside. I'm often outside for 3-5 hours at a time and 8 hours is not unusual.
I find these to be way overrated and not comparable to gloves I would consider of a warmer outdoor temp rating. If you suffer from damp hands (I do), then these gloves just don't seem to wick moisture away well. I find that I get cold in about 1 hour of using these and that I am very cold within 90 minutes to two hours. Glove liners don't seem to make a difference. My feet are warm, my core body is warm, but my hands - and especially fingers - are just frozen in these gloves.
On the other hand, Cloudveil Spacewalk or Cloudveil RPK gloves are much warmer, wick better and just do a better job in spite of the fact that they are rated for warmer weather. Another good choice is the Marmot Randonnee glove although warm, it isn't as durable.
I'd recommend the Cloudveil Black Ice Glove instead for deep cold applications or one of the Cloudveil mitts.
These gloves don't measure up, in my opinion. I've had them all and these are not "top of the heap" based on my experience.

I've had 3 pairs of these. The first two pairs were because they tore out between the fingers (index and middle finger). I'm hard on gloves, but these started tearing in the first two weeks of use.

However, these are warm. My wife also has them and has not had the durability problem that I have had. I must just have bionic fingers or something. ;)

I give them high marks for warmth and it would be higher if they were more durable.

Cloudveil makes terrific gloves and I depend on them as a ski patroller. I really like these spacewalk gloves (the RPK gloves are another great choice).

They are very warm, very light, and have a great wicking liner (I have perennially damp hands) that dry really fast with a few minutes on a hair dryer.

Highly recommended.

J