can I ask you is there a big difference if you would like to drive in winter conditions with winter tires like Pirelli Scorpion snow&ice (snow and light of road in the woods-roads) between 275/40/20 and 255/50/19?

The narrower tyres seem to be better. Over here, we get a document which tells what can and cannot be fitted in the way of tyres. The winter tyre width seem to be either the same as the summer tyre width OR narrower.

For example, if your tyre has a 20 inch width for a summer tyre, it seems that you can fit that width for a winter tyre or a 19 inch tyre. Personally, for snow and light off road use, I would go for the narrower fitting tyre due to the theory of the weight of the vehicle being concentrated in a slightly smaller area thereby giving greater penetration through any loose stuff on a "hopefully" harder surface underneath