This is really funny because my experience is the inverse of yours!
My 826 had lived most of it's life on the IH 30 and I continued with it but it slurped though the better part of a case in one season. I switched it over the R-T 15W40 and it went from 6-7 qts. a season to 1-2. It wasn't all the oil, I'm sure, because I work it alot harder than the PO did (at least in the 10 years before I bought it). The Neuss engines like being worked hard rather than idling around. I also have some very good UOAs on R-T. All my stuff is on CJ-4 now, two tractors, one older diesel pickup and some small engines. It works well with the ULSD and, as I said, the UOAs have been superb. Not afraid of using CJ-4 in combo with ULSD, but I would want a CI-4 with LSD or the older stuff.