I started using 0 40 after GM disaster I looked into it seems they’ve been using it in Europe for quite some time. The reason not so much here in the US is because of the EPA standards with MPG and the government’s ratings that have to be met. I live in a cold climate so zero would be great...
Depending on the ambient temperature where you live has a lot to do with the first number in the oil viscosity, but you can’t tell the difference between a 30 weight or a 40 weight oil when the engine is warmed up I don’t care who you are or what you’re driving.