After living in the Alaskan interior for a decade and currently in the upper Midwest of the U.S., I fail to understand why whether a 5w40 vs a 15w40 such an issue for cold weather. For this very reason, oil pan heater pads and inserts were made. An oil pan heater is darn cost effective and uses far less electricity than any block heater. After the engine warms up, there is no flow problem, in my experience, even at -70F. The oil is warm and flowing quite nicely. Once temps get down to or below 20F, I plug in the oil pan heater, block heater when it gets down below 10F. Though using a 15w40 syn blend now, I have used 15w40 dino oils in some pretty nasty climates for decades and never had any issues with cold flow problems. Heat will rise from the oil and into the block when using a oil pan heater, so plugging in the block heater is less necessary unless temps get down extreme. Diesel fuel related issues are more of a problem in cold temps than oil. Now.... a less than $100 oil pan heater and a cost effective oil, or no oil pan heater and a high priced boutique oil that will cost more over time. Not a tough decision. Even if I was using a high ticket oil, I would still use the oil pan heater. Best investment that can be made by any vehicle owner.