I prefer wearing a longsleeved top if I can get away with it, but for rides that vary between shortsleeve temps and longsleeve temps arm warmers are very handy. Just push them down when you get warm, pull them back up when you feel chilly. They come in different weights, the ones I have (Assos) are fleecelined and thicker than the sleeves on my longsleeved jerseys, and quite windresistant.
I'd typically wear a thin short-sleeve layer under my jersey as well, fine wool if it's wettish out, synthetic if I'm planning to sweat a lot. And I'd prefer a wind vest as a spare to a full wind shell. I tend to get damp under wind shells, unless they have lots of vents or preferably a mesh back.
My dh calls this the "module look"
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Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett