Bro, technically speaking what you have mentioned is 100% accurate.
But somehow I have felt that 20W-40 is less viscous in practical. Before LM and ZIC 20W-40, I used ZIC 20W-50 the yellow bottle (1-ltr) packing. It used to work good in my 70cc but Sprinter looked like had no love with this oil, heavy ride and heating issue was there.
Then I used Castrol Active 20W-50 and 20W-40. 20W-50 was more long lasting but 20W-40 was more active, pick was sharp and even lighter ride. My Sprinter immediately used to tell me that Saeen, 20W-40, 1000km ker chuka hai please fresh oil daalo :).
But again for me LM has no comparison at this moment.