Performance is fantastic, frozen fingers is miserable. We even have a tanis heater on our jet, which is a real luxury, and both planes go in a hangar everywhere we stop. The C421 is a nightmare in ground temps below about -15'C. Struggles to start, and the engines are so sensitive in descent its a real PIA. I try to avoid using it when it gets that cold. This winter hasn't been so cold, which is nice, and the C421 has been down for an engine change, which is even nicer..
Have you come across the post on "Icepilots" yet? A programme about Buffalo Airways who operate DC3s and other big round-engine birds out of Yellowknife and the North West Territories. Fascinating sceries, and would probably answer all your questions about cold weather operations.