Well, in your last few post you repeatedly mentioned your satisfaction about 5w-50.
Ok, what if your engine oil needs cst less than 15 at 100'C, then will you be using xW-50 in your car ?
If so, then it would be no wise decision at all.
The 2nd number in viscosity is 50, which means at high temperature the oil will NOT be thin enough. Means will remain more viscose. Means more resistance to flow.
Now technically in the hot summer (when engine is already working at high temps.), you should give it low viscose oil so that it work smooth & easy. You are feeding it xW-50 which means you are giving tough time to work.
No one uses 20w-50 oil in USA, Australia, etc. Because the oil does not get thin enough at high temp and gives hard time for engine to work.
But in Asia & Africa people are using this oil (20w-50) because it will take some time to understand. And its also one of the reasons here Cars visit workshops more often.