I also own a high milage Euro N52B25 with 230k miles. In europe they where specd for LL04 5w30.
I have good results with shell (pennzoil) 5w30 GTL oil in my n52. I even heard people running them on 0w30 without any problems.
https://bobistheoilguy.com/forums/t...5w30-pennzoil-euro-l-review-with-pics.334248/
Car is driven hard for long distances with and has seen 15k ocis all its life.
The euro n52s have an oil/water heat exchanger which heats up the oil faster, as far as i know the US models dont have that so thinner oil in your climate would be beneficial.
I know that in US they where specced for ll01 but dont know if 5w30 or 0w30 will harm them? Technical wise they are the exact same engines.
I dont know why they did 5w40 for us and 5w30 for europe, i thought it had to do with wat was availbe at the time and in europe the diesels also used 5w30 c3 oil for the diesels so it was easier to have in bulk.