If you are sweating during the winter while riding...you are killing yourself. Sweat is the eveil enemy,. Any sweat at all will zap the heat away from your body and leave setting in an ugly situation. I always go for one thing first, no sweat. I would rather be chilly than be sweating. What I'm about to say will sound very controversial but it's a fact.
What do I weat down to +15 degrees F when their is little wind:
Feet: Regular cycling shoes with booties with wool socks on the feet. Right now I am wearing an extra pair of Wal-Mart style lightweight thermal socks only to try to keep any seeping from the darn rash I have from getting on the wool socks.
Legs: Cycling shorts with single layer nylon windpants. Never thought I would do something like that last winter but this winter anything more is too much. I learnt this little trick thanks to the rash.
Upper Body: A Duofold Varitherm top, zip up neck(no longer made) and a double layer nylon windjacket..
Hands: Pop top ragged wool mittens.
Head: Cotton sweat band and a fleece ski 'band' for ear protection.
When the temperature gets around 30 I find I will sweat between the shoulder blades on the back, not a good sign, and I'll also sweat down where the elastic is on the cycling shorts. The front of me stays nice and dry because of the wind hitting me from the front and since the heart is right behind the shoulder blades, I think, is the reason why I find myself sweating between the shoulder blades. The rest of body typically stays pretty much dry. The hands and feet in the beginning of a ride may get chilled but they warm and maintain themselves quite nicely after a few miles of riding.
Like I said at the top if your are sweating any at all...your killing yourself. The objective to winter riding isn't to stay warm...it's to stay dry. I'm seeing that more and more with each and every passing day as I continue to ride in colder conditions with less and less clothing.
Last winter I would put on the homemade fleece pullover when the temperature dropped into the mid 20s. I don't know how I wasn't killing myself last winter. That was the stupidest thing I could have ever been doing. Yeah, I was sweating on the upper body. I would get home all nice and sweaty. This winter I'm not getting home sweaty, instead I'm getting home dry and comfortable. Last winter I would put the neoprene face mask on when it got into the mid 20s and lower. This year I'm waiting until it gets down to 10-15 degrees and finding it's not that bad. Last winter I was wearing cycling tights, no insulation in the tights pretty much 40 degrees and below. This winter I'm wearing cycling shorts until it gets to 15 heck on a calm day even down to around 10 degrees. Around 10-12 degrees on New Years night I was riding home...after dark, and my legs were chilled. I found myself saying I'm not sure I would feel comfortable riding any lower than that without having more protection on.
The secret isn't to wear the clothes but to have the clothes available to put on in case you need them. For the first time, on NYD I found myself actually carrying spare clothing with me. I normally don't. I knew the weather conditions were right at the breakpoint thanks to the wind. I wasn't going to press my luck and hope it didn't run out, so I carried the extra clothing with me(fleece pullover, neoprene hood, longjohns). I did end up putting on the fleece and face mask after 14 miles but I took the face mask off on the way home even though the temps were continuing to drop I had a tailwind so I wasn't being effected by the wind like I was on the way out.
Learn to play with what you wear. Don't listen to what everyone tells is the right thing to wear...find out for yourself. Go prepared and don't be afraid to try wearing less while carrying the spare clothing with you. You may very well find out that you don't need half of what you have on to keep you warm.
Again I'll say what I've reiterated several times. It's not about staying warm...it's about staying dry. Sweat kills this time of the year.