Low temperature test with 625xt. 
I'm used GH-625xt on every time when I do cross country skiing this year (about 30h so far) and weather was more or less cold. I have had weared watch outer side of jacket sleeve, so it is not covered with anything and it is directly affected to cold outside temperature.
It was working very fine all the time. Today was coldest day and I did 1h 30min training when temperature was -19 degrees Celsius. Only notable thing was, when changed pages, display changed slower than normally. But for example time and hrm was very readable all the time and that little slowness of display refreshing doesn't matter any harm.
So, it seems that this model as well is very suitable for winter sport activities.
Rookie