I don't think it is necessary to vary from MFG. recommend oil weight range. I think most of that belief comes from the good ol' days when oil was less sophisticated, engine tolerances were greater and less consistent. In extremely cold climates using lighter weights was common and it wasn't uncommon to use heavier weights when the blue cloud out the back stopped traffic.

I know I can randomly ask 100 people about why they use a particular brand and their rationale will be based on nothing other than it was recommended by someone they think should know or they have had good experiences with the brand.

There are studies that rate the brands. Some are more credible than others but since there are many different winners in the various tests it is easy to use a study to validate our brand choices.

Most of us have a brand we swear by. The reality is that there are many brands that meet MFG. specs so most of us have made a valid reason to believe in that brand.

I think the oil and filter change interval is the secret to how the inside of the engine looks after 100,000 miles and I would be extremely skeptical of anyone saying an engine problem was because I was using the wrong in spec oil.

__________________
X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas