I still don't subscribe to the idea that a 0W-20 is always superior to a 5W-20. The only time I think that's applicable is when cranking in freezing temperatures.
Let's take a couple 20 grades with the same KV100.
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I have a very hard time believing that flow is going to differ much anywhere above 0°C with these two oils. I think any difference would be trivial to even mention. The traction differences in the bearings between quality of base oils would likely have a greater impact on oil flow.
I mean, your own graph shows my point, up to ~60c.. There is substantial differences in viscosity between 0c and 60c. Everyone in the US basically, lives below 140f ambient temperature. With below 0C being regular for the majority of US and Canada, and still occasionally in most of the US, except for very southern states. Which, again with the same HTHS, even in the most southern states, there is at worse case scenario - no differences between 5w20 and 0w20. At best case, you're going to be getting a better product.
And you can see my previous study on piston ring wear.
But this entire conversation is absolutely trivial to begin with. The fact this has gone on this long, is absurd.