I have a 1500 Chevy pickup that has 217k miles on it now and has been on Pennzoil LL 15w40 for the first 90k miles in PA. Yes winters also. Then when i moved to NC and bought the truck from my dad, i also ran Rotella and ST 15w40 in it up to about 200k miles. About last year, i switched it to dino 10w30 after reading thru BITOG for a while. I do fell it start up faster with the 10w30 in the winter but honestly i dont notice the gas mileage at all, but i do most of my driving on the highway and work 17 miles away so the engine gets good and warmed up. i do think you would notice it, if you made a lot of short trips. There are others on this site that run nothing but 15w40s and 15w50s in everything and have great luck. When i lived in PA on our farm, seems like everything got wolfs head 10w30 or rotella. I know plenty of people there that use nothing but rotella in everything. I think it depends on your situation whether it would benefit your or not. The new T6 is an awesome fit for someone looking for a 5w40 for there gasser. The 100C viscosity came down to 14.2 and it flows pretty good at cold temps. The ZDDP has come down to about 1200 in the CJ oils so compared to the CI HDEOs of yesterday that had hot viscosities of 15.5 on avg and ZDDP of 1450 on avg, these are nice HD gas engine oils. If your vehicle does many long trips or is a work truck that spends a lot of its time hot, use these with confidence. Im not claiming to know if they would realistically help your engine last longer but they would at very least work very well.