Freaking out about different ILSAC grades is really silly, engines rated for resource conserving oils run fine on slightly thicker oils.
While the HM M1 10w30 is actually a high quality a3 with a3.5or higher HTHS, the differences are minimal. You can run 10w30 with confidence and would only worry if your temperatures started to drop itowards zero.. Run the 5w20 with fortitude and confidence if you like as well. Nothing is wrong with that viscosity, 5w20 can be built really strong it is a great selection.
I prefer to avoid 0w20s not because of the viscosity, but due to the fact that they are exempt from a specific deposit formation test..that does not sit well with me.
If by chance your driving habits and environment are well outside the norm, a thicker oil can be beneficial and many manufacturers actually recommend it in those circumstances as a more suitable oil for the service.
Idling around in city traffic does not put a large strain on the engine oil temperature regardless of ambient temperature.
Driving at high rpms for sustained periods does create a strain on the oil temperature and can lead to relying on boundary lubrication.
These situations can happen due to speed, gearing, or lower gear selection for towing. My Tacoma engine likes to hang around 3500rpms at 80 mph where I spend a few hours at a time on my l9mg bi weekly commutes, when it is not doing that it is running caliche roads in 4wd and choking on dust. Created by water and oil trucks.
My 4Runner like to runner higher rpms when a boat is behind it, or it is climbing mountain passes. Other wise when I ,a not using it wife uses it for groceries and taking dogs to the vet. But 0w40stays in for me.
If all they did was run around town..I don’t think I would have sought out the thicker oils I run.