Looking at the forecasts, for the week I'm away over Christmas, the temperatures won't even get close to freezing, so I'm going to risk it, and take the Kaffenback, not the snow bike (with studded tyres).
This of course means it'll start snowing tomorrow!
The current forecast temperatures do seem to be dropping in a weeks time, so it could yet be a cold and frosty New Year holiday. There's no snow currently being forecast for that period, but it's right at the limits of the forecast, so anything could happen.