I'm of the fit for purpose crowd. My 98 came filled with M1 and of course has the ad in the trunk. SO when I changed the first time I used the recommendation and filled with the M1 0W-40. When I inspected the filter there was a lot of brown and some green paddle pieces. With the new M1 there was still a lot of startup rattle. I figured had to be something better. So started research. I live in sunny Cali where temps in the dead of winter rarely get below 20 deg f. Obviously 0W is not required and by the startup noise it was time for a change. To minimize tensioner bleed down and reduce viscosity modifiers a 20W fit the bill but 10W-40 was good. Switched to Castrol Edge 10W-40. Immediately noticed FAR less startup rattle even after 2 weeks sitting. First pic is of some of the filter debris after M1 at 88.9k. Second pic is filter debris after CE 10W-40 at 93k. Both changes at 4100 mi. Much less paddle debris now. I found total of 4 pieces. Oh and NO metal on Mag plug or filtermag. I was happy with the CE but was considering the JGDT 40. Due to availability issues I switched to JGDT40. I'd be happier if it was 10W but who knows maybe I'll find myself in Colorado again at 30 below. Next change will be on JGDT40.
Personally if you never try anything else, How can you know what's best?