The original SAE paper on 0w20 development was done for hypothesis testing on fuel economy differences.
The paper is here:
www.sae.org
It is $40.
I bought it and read it. It is not a difficult read.
Fuel economy improved slightly and according to the
specific drive cycle tests; engine wear was similar to both 5w20 and 5w30.
So no definitive conclusions vs 0w40 ( wear could be less than both 5w30 and 0w20).
The engines tested were normally specified with 5w20 or 5w30. Changing to 0w20 in this scenario isn’t as big of a change as going from 0w40 to 0w20. They are also a radically different engine and powertrain ( transmission gearing and loading) than a 6.2 ( or 5.3).
So it is a factual matter that 0w20 was designed for incremental fuel economy gains.
The testing isn’t totally applicable to a direct injection v8 that is heavily laden with 6000lbs.
So conclusions about engine wear based on this paper and its results is unwise.
If people are highly motivated they can follow the method in this video to compare 0w20 to 0w40.
To do this you would need the appropriate machine design text to get the right minimum flow thickness charts . On top of the right dimensions for bearings. And you have to get the right viscosity units in terms of reyn.
the point is you can accurately calculate the viscosity required for max load bearing capacity ( in a worst case scenario of high load and low rpm).
When I did this I found that 0w20 had a small margin of safety ( oil viscosity degradation ) for 5.3 . 5w30 had a good margin of safety for 5.3 ( larger degradation of oil viscosity).
I found no margin of safety for 6.2 with 0w20. In fact 0w20 was a good bit lower than viscosity needed for max bearing load.
5w30 is a bit under viscosity needed for max bearing load on 6.2. 0w40 had a small margin of safety for 6.2.