This in anecdotal but perhaps this a bit of info that is helpful.
I'm running my '97 Explorer since day one and it's still churning strong as it will cross the 300k threshold before the end of the month. From the inception, it has had a single change of dino and the rest has always been synthetic oils and M1 filters once those became available.
In terms of specific types of syn, it has run on M1 5w-30 for probably the vast, vast majority of the time with a few changes of GC tossed in a few years ago when it was all the rage. Now I still run a syn 5w-30 but it's a mix of Castrol, PU or usually M1 at the same 7,500 mile intervals over the last 100-150k miles. Walmart is my friend.
At each smog check the output is still within factory specs for what a new car should put out according to the tech, and last year, my home state issued me a notice to have an off year smog check because a vehicle this old falls into a likely gross polluter category. Once again, the tech said I'm putting out so little pollutants that it seems like a new vehicle. The mileage remains consistent for so many years I can't recall, there are no leaks, and it still burns the same 1/2 qt every 5k it always has. The infamous Eyeball In The Fill Cap test shows a bright timing chain, no sludge and a nice silvery shine like we've all seen here on good cars without sludge. It's picture perfect.
So my point is this - The rest of the truck is falling apart and going to die long before the engine does. Transmission, transfer case, rear hatch, door switches, rust, wiper assembly and all the other indicia of a car that's starting the home plate slide but the engine is running like a champ.
At some point, as others have said here over the years, we'll manage to keep the engine alive and purring but rest of the car will die first. My advice is to pick any quality syn and filter, change it around 7.5k or whatever your analysis says you can do and call it a day. Go to a hockey game, fishing, to the shooting range but there's no reason to get antsy over the engine and the oil. It will not matter in the long run.
