Those are some really cold temperatures.  Seldom see temperatures that low on our farm.  I don't think we've ever experienced winter kill on our farm.  For one, our temperatures don't get that low.  Probably because of our proximity to Lake Michigan.  The Lake tempers our extremes in temperatures.  Also, and probably of greater importance, we almost always have adequate snow cover.  With enough snow cover, wheat can probably withstand any temperature.

Did this wheat have any snow cover? 

I believe certain varieties of wheat have better winter hardiness than others.  How does your particular variety rate for winter hardiness?

gordon