[jparnes1]

Back a couple of years ago when BMW used castrol as their BMW labeled oil, they recommended castrol as an acceptable alternative. But it was the castrol euro formula, which was 0W-40.
My point about the oil viscosity is that 0W-40 is thicker at full operating temp then 5W-30 because a 40 weight oil is more viscous than a 30 weight. Your subjective findings about sound and smoothness aside, that is the property of these oils.
In Europe, the 5W-30 oils made by European companies are LL-04 (Check Amsoil, Elf, liqui-moly, etc). LL-04 oils are made for cars running on low sulfur gasoline, which we don't have in the US. This is why 0W-40 is recommended here as an alternative, because it's the required LL-01 spec.
Conversations about motor oils always draws a lot of opinions. Use what you like.