I also have the B&S 5w20 weight reccomendation. Weird. They want straight 30 weight if operated above freezing. Hello? It's a snowblower!!!
Typically the coldest winter weather does not bring snow, it has to be at least 10'F where I live to have enough drama to precipitate.
Doing fine with valvo syn 5w30. Like everyone else, I run the thing at max power all the time. Get the muffler glowing cherry red.
My 1978 briggs generator says to cut the oil, I forget what grade, with 10% kerosene when it gets real cold. Hmm... no!