For me, the changes from 15 from 25 degrees F is I consider a face covering around 15 degrees or so (I wear a nomex face mask) and I wear lobster gloves not regular gloves at that temp. When I gets around zero, l go with another "level" of covering (mittens and headwind wind pants over my heaviest tights, and maybe googles over my glasses).
Lobster gloves let you shift, though they are more clumsy. My winter bikes have had old fashioned thumb shifters that let me shift even in heavy mittens.