You might also check with a local oil supplier for products. I have a Cummins ISX and am using a 50% synthetic blend CJ-4 under the supplier's label, delivered to my house at $9 a gallon cost. The engine usually runs around 145,000 miles a year, gets 30,000 mile OCI's, and now has roughly 671,000 miles on it. Last UOA on the oil at just under 30,000 miles was 11 ppm on iron, 2 ppm on lead, .1 on soot. Using a bypass filter on it as well. For extreme cold when the engine sits, I have a heater pad on the oil pan and block heater. Always has started great even down to -28F on a 15w40 oil. Since engine and oil start out warm, no need for a 0w40 or 5w40. Even if using a lighter oil, a heater pad on the pan is cheap and easy to install. Engine warms up faster. Got hooked on using them when I lived in Alaska for 10 years.
For winter fuel treatment, I have become partial over the last two winters to Amsoil's Diesel Concentrate plus Cold Flow Improver. I have had some better results from it than the Power Service, Howe's Lubricator, and FPPF I used before in the winter, especially when fuel sits in the cold for a while. Not a case study, for sure, just anecdotal.