Engine Oil Weight (Viscosity)

Any time you have a blend of anything the window that the blend might be at if one looks at something like viscosity vs temperature is going to get smaller and smaller.
If you are driving a vehicle in weather colder than freezing you want that window be as large as you can get it.
The same as if you are driving a vehicle at temperatures at 100 degrees you want that window to be as large as it can be.
The variables given as caution in technical manuals have give precautions to take into consideration at various temperature levels. How those windows were determined were not give other than this
5W does not provide adequate lubrication when the temperatures exceed a given value.
As Oil is a mix and I don't drive in area's where I need to protect an engine at -10 degrees or something like that, I do not want nor need that oil for protection at -10 degrees. And I do not need the mix diluted for narrow windows at the temperatures I do drive in.
On top of that I have seen the results of having done so and I am not going to risk an engine I have built using oils that have caused that damage.
So as far as I am concerned, there will be no oil in my cars or engines that are rated at functional under 32 degrees.
An engine with a steady diet of 5W20 is a dead player at 100,000 miles. An engine using oil comparable to the temperature ranges it is used in, is good for untold 100,000's of miles with out an oil related failure.
Your charts to not show that. But the engines do. At least the ones I have seen have.

Interesting that not of the charts seem to include 5W-20, so you would have to draw the conclusion that it doesn't have enough of a viscosity spread to be good for anything.

Really talking about ambient temps of 100F is irrelevant in terms of what is happening inside the engine where the oil temperature is going to be somewhere around 180-220F once the engine is up to operating temperature. A SAE 20 grade oil will have a viscosity between 5.6 and 9.3 at 100C (212F) which is about half that of a 40 grade oil at the same temperature.

The other word of caution is not so much memory but more the fact that the viscosity improvers can break down over time so the oil can loose some of it's multi viscosity capability.

I have had the experience where I have suffered component failure that has been attributed to running 20W-50 oil, with the recommendation that I should run 5W-30 preferrend (max 10W-40) to avoid this happening again.

If I hadn't had this particular problem, I would probably still be running 20W-50 oil.

the chart may be missing recent synthetic multi viscosity oils. as WesternRed mentioned, 0w-20 and 5w-20... plus there are two versions of Pennzoil Platinum, one is strictly synthetic and the other is Dino, both carry the same viscosity rating.

as for 0w over 5w on 20w oils, 0w-20 is to allow better economy, though it will allow for added oil consumption.

going by what our 09 Honda came with 5w-20 and what was officially changed to 0w-20 in 11, it seems that Honda had ring issues early on and was not discovered much later in production. I have switched to 0w-20 since 11 when the ODO had 12.5K, and never had any issues with oil consumption and wear. though I did not go by Maintenance Minder, which many peeps use to tell them when to change the oil. I would change the oil, being full synthetic, once a year in late March. My maintenance minder would be around 50% most of the time, meaning I had 40% more life, by the computers judgement. I wonder how much extra wear is going on for peeps who use multi viscosity oil beyond a year because they think synthetic oil and maintenance minder will allow engines to run 2x longer between oil changes.