At these temperatures a leather jacket with just a wool or cotton liner will probably serve you much better. Or get a D-1 or B-6 and wear it with a t-shirt. An Irvin should be nearly unbearable at night and totally out of the question during the day, unless your fridge is large enough for you to get into it.
Exactly my thoughts!
I have owned a B3 for the past 6 or 7 years and have only been able to wear it a couple of times, living in London, where we get snow and freezing temperatures pretty much every winter!
To me a sheepskin jacket is unwearable in anything higher than -5c. I tried wearing it last year in 0c and i was a sweaty mess after walking 100m...
Unless you are very very VERY cold all the time, i doubt you will ever have the opportunity to wear it!