I use:

Nylon ski glove shell procured from discount ski gloves. Reasonably well made shell but not to high standard of expensive gloves.
All lining and insulation removed from the shell.
Medium thick unlined polar fleece glove inside Shell.

Medium overall dexterity.
Good dexterity for shifting mountain bike type shifters and gripping handlebar. And most all riding tasks.
inadequate dexterity for fixing flat tire or zipping standard jacket zippers.

50-40 F -> too warm
40-30 F -> just about right but hands feel slightly warm
30-20 F -> hand comfortably warm, fingertip ends may get slightly cool if not riding hard.
20-10 F -> hands stay warm enough to ride at brisk pace but fingertips get cold but maintain adequate dexterity for riding

My hands are generally sensitive to wind chill but don't require much insulation while riding at my usual pace. In general it is easy for me to keep my hands warm compared to my feet. I neither have hands that are tough in the cold or hard to keep warm.

Pros:

Easy to separate and dry out after rides.
Dry out quickly.
Relatively cheap to buy.
Work well over large range of temps.
Very good wind resistance.

Cons:

Not as breathable as I'd like.
Not warm enough for below 10-15 F range.
Less dexterity than thin cycle gloves.