I am believing that for many, the level of insolubles becomes the limiting factor in drain intervals, not TBN. A great filter will help (controversial I know). We also know that things like LC and FP help a lot. For us that want to use straight oil with no adds and spin-on filters, I'm thinking there is something to these long-life formulas. We seem to be seeing reduced solids with M1 0W-40 ?? Not a tremendous amount of data, but.... I'm beginning to think some of these syns that meet certain long life specs. will get me to where I want to be better than just running M1 10-30. A syn can be great, but if your solids limit you, then not so great. There is something real about these long life specs. like the 0W-40 has. What say yea??