Your charts prove that low viscosity motor oils reduce total engine
friction but this does not address
wear at all because friction and wear are sometimes not very correlated in the context of internal combustion engines.
More support for higher viscosity directly from your linked Toyota study:
One possible factor contributing to the increases infuel consumption is the expansion of boundary lubrication areas due to decreases in viscosity specifically after engine warm-up.
It is already proven that mixed and boundary lubrication regime applies at low speed higher load such as those frequently encountered when cruising at low RPM (due to transmission gearing optimized for fuel efficiency).
For preventing wear in mixed and boundary conditions, where metal-to-metal contact is more likely, the viscosity of the motor oil is crucial. In these conditions, a higher viscosity oil is generally more suitable because it forms a thicker lubricating film that can better protect surfaces from wear.
Therefore, between two otherwise identical motor oils with a 0w rating but different viscosities, the one with the higher viscosity would be more suitable for preventing wear in mixed and boundary conditions. This is because the thicker oil film can more effectively keep surfaces separated and reduce direct metal-to-metal contact, thereby minimizing wear.
In a sense these low viscosity motor oils are better suited for saving fuel with good wear prevention at higher speed freeway operation because at higher RPM hydrodynamic lubrication regime applies.
Over the past 20 years, the clearances for Toyota's journal bearings have remained relatively consistent, reflecting standard practices in engine design and manufacturing. The typical range for main bearing clearances in modern Toyota engines is approximately 0.0012 to 0.0025 inches. For example, the 2AZ-FE engine, widely used in various Toyota models, specifies main bearing oil clearances ranging from 0.0007 to 0.0016 inches.
In specific rebuild contexts, such as the 1ZZ-FE engine, rod bearing clearances have been measured around 0.002 inches, which aligns with the general guidelines of maintaining clearances within a narrow and precise range to ensure optimal performance and longevity.
Overall, while there have been some minor adjustments and refinements in bearing materials and manufacturing precision, the fundamental specifications for bearing clearances in Toyota engines have not seen significant changes over the last two decades
If this is all true, then the main consideration for using low viscosity motor oil in passenger car engines which operate at low speed and higher load must be primarily fuel efficiency and not longevity.
Somewhat surprisingly it seems to me that these low viscosity motor oils are superior for racing applications where high speed engine operation means the more of the engine is operating in the hydrodynamic lubrication regime.