You know what? I have no idea!
It seems to vary. I live in a place of moderate extremes, if that makes sense -- i.e. we have extreme cold and heat by some people's standards, but moderated by the lake effect. Which also increases humidity. And wind! Which in turn makes it more difficult to judge.
I get Reynaud's in my fingers, mostly when the temps are really low, but sometimes when it's hot and my hands are at the wrong angle. (Go figure).
I find AC deadly cold. I literally feel like I'm in a morgue the way most places set it!
But I live without AC, and mostly have to put a fan on in summer or I'd die of heat! Working at home in temps of between 24-26 I'd likely wear longer pants/jeans, sandals, a lightweight sweater (cotton). Once it gets above 26, the humidex likely makes it feel more like 30 (and sometimes up to 38 or so) in which case I'm in a light sleeveless top and shorts or dress, and melting miserably, yet also thrilled at the fact that it is warm out for a change!
We keep our house at about 22 or 23 in winter. Indoors, while working, I will wear jeans, socks, warm slippers, a cami, a wool sweater plus scarf. Outside I will be wearing a coat, obviously, plus hat, gloves, etc. because temps will be below freezing.
I tend to start wearing booties and/or socks when it gets around 17 or 18 in the fall, and that is the approximate temp in the spring where I feel like I can wear my closed shoes without socks, assuming I'm warm elsewhere.
I agree with those who say that activity levels make a difference. And also with Traci's comment about layers. I find a cami, a thin wool layer, a scarf and a windproof coat go a long way outdoors.
