I had the same dilemma. I could only get Pirelli Sottozero in the 19/20' and the reviews were not good and it would cost $1600 plus fitting etc
I went with the 829M and the Alpin from BMW for $3440.
We are in NYC and you can get the occasional blizzard so figured I would be better off on the 19' smaller tires but if you're only really dealing with rain I would imagine you should be fine with just the tires only and should be able to handle a bit of snow too quite easily. I think one of the issues with the bigger wheels is snow getting stuck in the arches but also smaller slimmer wheels cut through snow much better than wide huge wheels
The 829M's look good for a snow set up in this thread!
https://g80.bimmerpost.com/forums/sh....php?t=1800593