if you're looking to Tracksmith for winter running pants, they offer better options than what you've listed:
the Brighton pant is a stiffer, more wind resistant, thinner but water-repellant choice. those are currently on sale and can be layered with tights underneath
they also tend to sell a heavier, more winterized set that debuts in Januarys, the NDO pants. they're a softer material than the Brighton and come with more pockets and ankle cuffs, but will hold onto moisture. I think they're a lot like the Session pants, but built for winter instead of spring
I usually roll with just their tights until its below freezing, then add Brightons on top of the tights if it's precipitating or until its below 20, and then go with the NDO for anything beyond that