If I may, I like to add a couple of comments of real driving experience with the PA4 today in Toronto, Ont, Canada.
We just had a 15m snow storm past thru overnite and it was my first real snow encounter driving my M5 with PA4 on the local roads, almost unploughed. The overall traction for the tires are actually pretty good, but the car's dynamic traction control needs to kick in many, many times to help the tires to gain some grip on the pavement. I did not get stuck in any situation but I must say I need to disengage the 'MDM' system so that the DTC will not engage the brake as often as I like to.
Overall, I am satisified thus far even though it's only 1 real test run to-date.