I have Specialized gloves for the summer (open fingertips) and pearl izumi full finger gloves that I've been wearing recently and have kept me warm. I will switch to the MTB because they put quite a bit of sand on the roads and the amount of potholes increases tenfold in the winter months. Those tiny narrow tires have such a small contact patch that a few wet leaves or a patch of sand can put you down.
Also, if you're doing 20+ miles on roads and really enjoying it, you would be completely justified in spending a bit more for a higher performance bike from a legitimate bike shop. Just throwing it out there. For about a grand you can get a very nice aluminum frame Trek or alike which will transfer your effort to the road quite a bit better.
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