Ironthinker, from what I can find out here at this web site it looks to me like Pennzoil is probably the best OTC conventional motor oil. According to what people have been able to find out, the regular Pennzoil flows at low temperatures (there was a freezer test that indicated this), and protects about as well as any other motor oil. I have come across some negative information about the Castrol GTX and the Chevron Supreme, so this puts Pennzoil about in a class by itself.
For cold weather you could use Mobil 1, and then use the Pennzoil High Mileage in the summer months.