After spending a fair share of my life working as a farm hand. Cutting fire wood, tending cows, hunting.
A good pair of mittens are the warmest. A glove of the same insulating factor can let your finger get cold. In a glove each finger is on it's own, in a mitten they can keep each other warm.
A mitten is harder to work in. It makes using the controls a bit harder.
A short cuffed glove or mitten lets air get in between the glove/mitten and your sleeve. A good riding glove/mitten should have long gauntlets that have ample room to fit up over your sleeve. As air blows across your hand the gauntlet keeps the air from getting in your sleeve, the air flows up your arm instead.
Some of the best cold weather gear can be found at snowmobile dealers. There jackets, pants, suits and boots are designed to keep you warm and dry. They keep out the wind as well as the wet.
I have tried many gloves and mittens over the years and have found they all lack something, warth, dexterity. I recently got a pair of half breed glove/ mittens. They are like mittens but they are split in half so two finger go in each half.
They are much more nimble than mittens and warmer than gloves. I have used them out snowblowing and ice fishing in zero degree temps and even after a couple hours my hand are still warm.
If the roads where clear I would get one of the bikes out and see how wind resistant they are.
I have had several gloves/mittens work fine in the cold snowblowing or ice fishing but riding they need to be windproof to.
They cost me either $22 or $24.