I'm passing thru 10k on M1 0w20 in my '06 Mazda 6 - pretty much as I write this. Bought this car last summer. Put the M1 in the first wkend of the school year (three kids in elementary school). Ideally, I'd like to just drop a new fill in that first wkend of each school year. But that would mean taking this oil thru a hot summer, and maybe ending up at 14k or so. And I haven't added a drop of oil in the last 10k (still at the full mark). If I have the nerve to take it there (to one year), I could UOA it and I would have proof of concept (or lack thereof).
One OCI per year has always seemed the essence of efficiency to me, but pushing a 15k OCI in this gem of a car - man, I don't know.