I'm currently living in a country that had temperature swings from 25F to -40F in a matter of days.  I find these leggings to be great for 10f to around -10F.  Anything colder and I want my thicker cuddleduds, but these are great for most days.

I really like the length as well.  I am 5'6" with not overly-long legs and these are long enough to cup my heels.  Maybe other wouldn't like it, but I find it makes me feel quite snug.  Also, I am able to wear these leggings all day without getting overly warm and they still keep my toasty during my walk to and from work.  I would recommend them to anyone, though sometimes I wish they were a little thicker.