Thanks for posting this!
For what it's worth, I talked on the phone with a gentleman at Chevron Delo's Technical Support and asked why it was more important to reduce ZDDP and be SN rated, instead of staying with their previous levels. He told they're using new ashless additive technology that provides better protection that allows them to reduce ZDDP levels. My guess is all the major companies are roughly doing the same thing in their CK4 HDEOs.