for freezing weather, 5w40 or even 0w40 from Shell, Mobil or Caltex diesel rated oils.
the engine will spin really quick even in Siachen in December.
today its frozen in houston - my car had 1 inch thick ICE on it, ice not snow, temperature is -4 C and my mercedes which uses mobil1 0w40 started like it was summer. Quick, smooth and easy.