"Seeing as how this engine is relatively easy on oil, I don't know that there is a real benefit to using a 5w40 in this motor."
No, I don't think there is any real advantage in terms of viscosity either, but there are big advantages in terms of anti-wear protection, engine cleanliness, and capability of extended drains over a group II PCEO, although I'm comparing apples to oranges here.
"His current strategy of using whatever 5w30 an a 3 or 4000 mile interval likely has done no harm."
Sure, probably hasn't done a great deal of harm, but obviously there are better choices, and like I touched on before, Rotella will offer much better anti-wear protection as well as clean up some of the deposits/varnish the 5w-30's have left behind, as well as keeping new "stuff" from forming, even on something like 7500 mile intervals.
"Since there are very few UOA's that even begin to hint at an extedned capability on the Rotella T Syn and next to no UOA's using 40 weight oils in these motors, I'd be leery of pushing this oil with doing some testing myself."
Sure, I would do testing if this was my vehicle, but obviously, it's not, and he doesn't want to do analysis. But, with that said, I feel much more comfortable pushing the drain intervals with the Rotella than I would with a standard 5w-30 PCEO. The engine, although no real maintenance has been done to it, is in good running condition and does not leak coolant. In a modern, clean running engine like this, even with Rotella doing a great deal of "cleaning" on this first interval, I don't see a 7,500 mile interval being too far out there, given his driving habits of many highway miles.
"I say this since I currently run a 4.6 in my '99 F150, but am running Havoline 5w20 on 6000 mile intervals. I also use the Rotella T syn, but that goes in the Jeep Cherokee..."
I do feel that 5w-20's can protect in modern engines, but I absolutely can not stand dirty engine internals, and I firmly believe that over time, use of any mineral-based PCEO is gonna leave a great deal of deposits/varnish behind, even using a good oil and the "standard" 3,000 mile drain intervals.
BTW, sorry if I'm coming off to strong here and trying to act like I know everything. I don't...I just like "debating" with someone as to what the "best" choices are...you stating your opinions, and then myself stating mine.