I've been told that 0W-40 Mobil 1 actually has the characteristics of about 12W-40. It would work fine and would be my choice for temps below 4F.

The 30 weight Mobil 1 oils no longer use a true synthetic base. It's a long story but they changed to compete with Castrol who began using a petroleum base for their popular viscosity's and called it synthetic. The 40 and 50 weight Mobil 1 oils are true base 4 oils. Compare the pour points of the old 30 weight Mobil 1 oils with the current ones and you will see the new version has much higher pour points. Mercedes no longer approve the 30 weight Mobil 1 oils.

I've used 15W-50 Mobil 1 in my car in Minnesota winters but this wasn't my daily driver.

Quaker State is now part of a conglomerate who also owns Slick 50. If that doesn't tell you something I don't know what will. The last I heard the conglomerate had sold all it's processing plants and was buying oil from other suppliers. The good old days of Quaker State are long gone.