I've got 2 Jackets.
The warmest is not leather, believe it or not. It's the Tourmaster Intake Jacket. It is 3 layers; the out 2 are wearable as separate pieces. The outermost layer is a mesh jacket system that holds the elbow, shoulder and spin protectors. The next layer is a rain/wind blocker layer that is also wearable separately. Inside that rain/wind block is the thinsulate liner, you cannot wear the liner as a separate unit, but you can wear it with just the wind/rain block, or in combination with the whole system. This jacket is very versatile, and very, very warm. Actually warmer than my leather raiding jacket, which in all honesty I prefer wearing. Go figure.
My leather jacket is warm, but not as much so as the one mentioned above. My leather jacket is also a Tourmaster. It is the Coaster Series 2 Jacket. It has 4-5 zipper vents on it and a removable liner. It is very thick leather and it does block the wind very well. I guess the liner is just not thick enough to really keep you warm.
On the same note, invest in a good neck warmer. I don’t care how good your jacket is, if you don’t block the wind from going down into it, you’re not doing yourself any favors.
Good luck.