I second or third Sugoi Midzero/Subzero for those temps. I have only used UA Heatgear so can't compare Coldgear to Sugoi, but I have a lot of Sugoi pieces and would say that in general it is higher quality than UA. I would also be commando in tights in those temps. When it is much colder (sub 20) I usually wear running pants (tapered but looser than tights - Hind pretty much owns this market) with long underwear (commando under that though).