I've got dedicated 18" M rims for snows - Michelin Pilot Alpin. Great ride and handling, very good in light to medium(5-6") snow. For heavy snow, Range Rover. Wouldn't do runflats if you paid me (which BMW did and I replaced them with Pilot Super Sports). Really hurts the cars performance, IMO.
550ix, Dark Graphite Metallic II, M-package, Dinan Stage 2, 20" wheels, conven pkge, cold weather pkge, Prem Pkge 2, Paddle Shifters, vent seat pkge, sport transm pkge, fold-dn rear seat, etc. Black Dakota Leather, Light Wood trim