Didn't see that you had double-posted this to both the English & German threads and replied their (in English) first. Oh, well.
We (I and friends) use Nokian snows almost exclusively here in New England. They aren't that common but from experience we've learned that they are the very best for snow. I highly recommend them as first choice if they will fit the car you have.
I tried to buy them in Belgium but could not. The distributor told me that they cannot buy them because the factory is worried that they will be grey marketed back to Scandinavia and Finland where they are made and where tyre prices are much, much higher.
The official reason was that they were not safe in the warmer climate because they were formulated for very cold conditions. But this is b.s. else they wouldn't sell them in the USA where the temps are much higher than anywhere in Europe. Nonetheless, I would be careful with them when it is very warm out (basically make sure you don't try to use the snows in the summer months).
Highly recommended for winter driving.
RC makes a valid point about making sure that the tyres will work with the Cayenne. Just as he suggests, you will need to look at the speed rating (which must be below the 270 km/h he quotes??) and the weight rating. Why not try to get Nokian to say that they are ok for the Cayenne? That might help if there is a problem. But personally, I think I would feel a little more comfortable than he going for these tyres if all of the specs make sense.
Hope this helps.
S.