It will be interesting to know.
What are your reasons to go from 0-40 to 5-30?.
In my father's BMW 330XD, they had been putting Castrol Edge 5-30, last week it reached 160.000 km, the mechanic recommended moving up to Motul 5-40 (also fully synthetic LL04 like the Castrol) as he thought 5-30 was starting to be too thin for this engine and mileage.
I was a bit reluctant to do so, for the reason posted before, but now it's done, so I guess we won't go back to the 5-30. Maybe Mobil 1 0-40 would be a better option for the winter, that's why I'm interested in why you want to change it with 5-30.
Regards.