knierman
Back in August during our trip to Colorado, it got down to 38°F one morning ride. When the body is used to Summer temps, this comes as a shock to the system. It’s usually 2-3 ~40° rides before I even want to think about getting outdoors once on a bike when it eventually gets below freezing. Then a couple of freeze-level rides before the body realizes it can handle a little bit more (less rather). Got in a good hour+ before the work week. 23° felt like a sweet spot. Two performance Tshirts, arm warmers, then a long sleeve wool jersey and I was fine and toasty. Toes are my worst problem, but they are expendable. Ride yer bike! 
yeah, toes are the worse….been riding with pedals and boots, that helps a ton, till it gets into single digits, then after a few hours a brisk run for a few minutes really helps.
I use a light performance T, a mid merino wool outer and a light wind vest (vented on the back) for 20 and above. From 10 and up I go with a full light wind shell (arms covered). Below 10…it depends on wind.
I really try to keep the moisture out and prefer to go with a vest to help to wick the moisture out the arms/sleeves.