Mitts (choppers) are much warmer than gloves for extreme cold. If you buy them a bit large you can manipulate the DIAD buttons while still keeping them on. They take some getting used to but once you figure out how to work the DIAD with them on there is no glove that can compare for warmth.
Thinsulate is superior to down, foam/fleece, BOA acrylic, cotton/flannel both for warmth and bulkiness. Consider how thick the Thinsulate is (150 to 400 gram) , and how it is distributed.
Keystone thumbs are critical for dexterity, comfort and durability.
Long insulated cuffs work well for drivers in extreme cold unless you are one who is constantly pulling them off and on.
The thickness of the leather used is critical for longevity.
I prefer the top of the line thinsulate lined Wells Lamont products (gloves above zero and mitts below zero).
The superior stitching, design and quality of materials make for comfortable, durable glove.
I have some thinsulate lined extreme cold work gloves from Superior glove coming to me as well. We will see if they stack up to the Wells Lamont gloves.