10W would be well within your winter temperature range. iirc it's good down to -12F. Definitely good down to 0F.
It also has less vii (vm) and typically much lower Noack than 5W-30's.
Regardless of oci, the less you burn, the better since you also mentioned cat ...
if I had to choose one oil for the rest of my life and in all our cars, it would be M1 EP 10W-30. 10W is ok for our winter temp range. c
I agree with all of this and especially the way it was said - logically and with physical/chemical reasoning included.
I differ at the M1 ___ 10w-30 step as I lean towards a different M1 flavor, but that's not as important as focusing on a narrower viscosity spread appropriate to your climate, low Noack, and robust HTHS. If you want robust oil, you start with the narrowest cold flow/full temp gap your climate tolerates on the low temperature end and your engine requires on the full-temp end (and this is NOT what's in your owner's manual, that's written for lawyers and local politics like CAFE). Most places, most engines, all over the world, it's 10w-30. Not 100%, but that's the default answer.
To butt-in on your question to him, keep in mind there is no "free lunch" anywhere - and that applies to supermarket promotions as well as oil viscosities. When you choose a 5w-30 vs. a 10w-30 where the cold start temps are not very, very low, you are sacrificing other desirable qualities in order to get that extreme cold flow. It has nothing to do with anything at normal temps, and many negatives.
Noack matters at all times - it matters any time the engine is actually running. The oil temps are not wholly uniform everywhere as a fraction of the oil is getting very hot in the rings, or under extreme pressure elsewhere. Noack matters in those spots, all the time. If you intend to never check the oil level or worry about thickening, then Noack is less important if you run a shorter OCI. There's just no free lunch, you have to think and balance things out.