The oil thins as it warms up...
What I tried to say is I see no real reason or benefit running 5w40 in my application in regards to where my car is and how I drive it. I'm currently on 5w30 and I'm ok with leaving it at that.
All I'm looking for here is low saps 5w30 oil with lower noack value. If I lived in Europe, I'd have more options but here my choices are limited.