I'v been running the 5W40, full syn, year 'round, for 10+ years and 150,000+ miles now.. up and down the Sierras, the Rocky's and across the dessert(s).
I run my 7.3 hard.. but I don't abuse it.
I change the Premo filter @t 6000 miles, add 1 quart. Change the oil/filter(s) @ 12,000 miles. (sooner if my SOTP tells me I should)
JMO guyz'n Galz.. but I think this WHOLE Oil thing.. has alota HYPE to it. (Mine'z better than yerz ?)
Joe