My wife's 1995 Villager has 191k miles on PCMO. Mostly dino, but some syn's intermittnetly along the way (experiments). But I've been using dino's for problably 160k of the 191K miles, and I'm committed to dinos every 5k miles from here to it's death (if it ever does die ...). I am convinced via UOA evidence that they are fully capable of any job I put them to, as long as I stay within their range of ability.
Our Villager engine is spotless inside (I know, because I had to pull the heads after she over-heated it when the water pump went out and she kept driving). The compression is great; no better or worse then before the over-heating incident. The seals are in good shape; no major leaks. All this on dino PCMO. I don't know that an HDEO would have done any better or worse, but at some point, it's just a moot point.
I've also had my (presiously owned) 1996 Vulcan 3.0 Taurus valve covers off after a full life of dino oil, and the heads were spotless (and Gary Allan can attest; he's seen the photo's). Further, the UOAs suggest the wear was well within acceptable limits.
Fundementally, I see many people "overbuy" their oil for a given application. Perhaps an HDEO would do "better", but to what point? If PCMO can run you past 250K miles (and there are plenty of evidentiary points proving this), then why spend the extra cost?
What most people don't understand is that there are three levels of oil: good, better, best. But that is NOT an indication of how well they do any task, rather it is how LONG they do that task. Syns don't protect against wear any "better" than a dino at 5k miles. Syns DO protect LONGER (more mileage) against wear. The same concept goes for cleaning an engine. If your engine only produces contaminants at a given rate, then any oil will do well until the add-pack is overwhelmed.
Will a dino HDEO do a "better" job in the engine than a PCMO? That depends upon how long you leave it in there. If you're going to OCI at "normal" OEM recommended rates, than I say a PCMO will do just fine, and there is no real advantage to using an HDEO. If you're going to extend the OCI, then HDEO or syn's with the bolstered add packs will survive longer.
Think of it this way:
a cheap dino oil will likely last 3k miles, but then give out
a quality dino PCMO oil will likely run at least 5k miles, maybe more
a quality dino HDEO may last 7.5k miles easily, but perhaps more
a quality synthetic would likely last 10k miles, likely more
any oil, combined with bypass filtration, will likely go well past 25k miles
Get the point? This is about how LONG you use the oil, not how much "better" one is over the other. For any given duration, you can either under or over utilize your oil.
You are under the same gross misconception that most people fall into; if some thing is good, then more is better! But ONLY if you use it in the correct perspective. If you use a premium group IV synthetic, but only for 5k miles, UOA evidence clearly shows that it does not protect or clean any "better" than a quality dino.
Now, I will define the term "cleanliness" as a matter of contamination that affects the performance of an engine in a detrimental state. I do not believe that every molecule of dirt of varnish is inherently evil and will bring untimely death to my ride. It is only the gross accumulation of contaminants, past the ability of any given oil to hold it in suspension, that makes for bad engine life. Yes, I've seen the wonders of marketing on the TV commercials, but I've also had my wife's engine apart, and I'm telling you that some small amount of dirt is simply a non-issue.
It's a matter of how you define "better". You won't get less wear or more cleaning using an HDEO versus a PCMO. But you'd likely get LONGER use of the product.