Not an out in the woods fun ride but did go around the hood ( a three mile loop around my neighborhood ). Mostly it was colder than I have tried with the Wolvhammer boots, 7F when I did the ride, still looking for sub zero.
At 7F, bike shifted fine, mineral oil brake fluid gave no problems ( still really like these Magura brakes ), and stayed toasty warm. I'm still wearing the same stuff I BC in where -14F plus wind was not an issue.
As I was finishing up the loop, I was actually starting to over heat.
Funny how that loop takes me about 12 minutes on my garage bike ( Trek FX ), this ride took me about 15 minutes. Definitely feel the fat tires in the snow.