I just got the Sugoi MidZeros and they worked well for running/walking around 30 degrees and also riding in the 40's.
If your butt gets cold in running tights, I highly recommend wool underwear. I never wear anything under my tights except when it gets really cold and I have found that my Ibex underwear makes a huge difference. I also wear my Ibex under my silk long underwear when I x country ski in really cold conditions.