I guess I can give my thought on this.
I had an X5 3.0 - always placed snows on it in the winter - now have an X5 4.8
same story - snows go on the same time as on the M cars -
some people think its insanity to place snows on an AWD vehicle. - I'm not one of them.
I will say - the AWD BMW's with snows - handle the white stuff amazing well. At times it is hard to even engage the traction control.
There is no question - they are far more stable than the RWD cars - in fact - they are really quite unstoppable - with the exception of ice - and black ice is really nasty.
But - I used to drive my M5 all the time in the winter - during big snows, sleet, you name it. It never let me down -
you need to pay attention. In fact sometimes, I am FAR more worried about the other drivers in their cars smashing into me - but it will safely get you to wherever you need to be