Agreed. We see a handful of sub zero degrees nights through the winter and I've always used 15w40 with excellent UOAs. Block heater and pan heater wired together, plugged in on a timer for 2 hours, start up, clean off windows and either hook up or drive off slowly.
The only real advantage I see synthetics as having aside from those who truly live in Arctic regions is extended drain intervals. But given the 15k intervals it's hard to justify the cost of synthetics given these engines will far out last the rest of the truck.