I’m really interested to learn more about your research, because these findings are interesting. If you can share some of your methodology it might shed light on the confusing findings.
The market observation I'll grant you. "different markets don't have identical motors with different tolerance" is a fair point, and the same engine getting 0W-20 here and 5W-30 in Europe or Australia hasn’t been well explained anywhere that I’ve seen. That's an argument about why the recommendation differs. It isn't yet an argument about what the oil is doing in the sump. So:
You wrote "HTHS is what causes the oil to break down BEFORE 10K." Can you walk me through that mechanism, and how you measured it? HTHS is a viscosity measurement taken at 150°C at a shear rate of one million reciprocal seconds. It's a number that describes the oil, the way a torque spec describes a bolt. What's the pathway you observed by which a measurement (HTHS) causes degradation? Oxidation, nitration, fuel dilution, TBN depletion, and permanent VII shear are processes. Which process are you actually pointing at when you state HTHS causes the oil to breakdown early?
Related: you list "~2.5-2.7 with 20 weights." SAE J300 sets the HTHS minimum for the SAE 20 grade at 2.6 and for SAE 30 at 2.9. A licensed xW-20 at 2.5 doesn't exist. Where did your 2.5 come from?
On "this breakdown typically occurs in the 6-7000 mile zone predictably," and "as was shown very nicely by analysis on this forum": how many samples, across how many engine families? And the one that matters more, what did the 30-weight UOAs from those same engines, same mileage, same driving pattern show? And more importantly, as asked above, what exactly did you observe break down? Without that comparison I don't see what the 6-7000 number is measured against.
"the oil is still 99% doing its job." 99 percent of what, and how did you measure it?
On the interval: you say moving to a 30 makes it "very safe to extend oil change interval to at least 7500 miles." What does the 30-weight have more of? Same detergent, same antioxidant package, same starting TBN, same dilution rate in the same engine. If viscosity grade sets the safe interval, what's the mechanism your research uncovered?
"has NO downside." What did you measure to establish that? Did fuel economy delta, cam phaser response time, and oil temperature all get measured as a part of your research? Phasers, chain tensioners, and AFM/DoD lifters are hydraulically actuated and calibrated around a viscosity, so I assume they were all carefully considered in your research.
"It is still the world standard." Japan is on 0W-16 and 0W-8 factory fill. Which standard are you talking about?
The filter point I think is well-proven, at least for cellulose media.
