I have conventional full flow and bypass filters on two vehicles running German Castrol...a MotorGuard on my Toyota truck (R22) and a Trasko T3/4-20s on the Supra (dual filter head). The full flow filters are changed at 4k, the MotorGuard (a roll of TP) 1st change at 1k (should last 3k from now on), and the Trasko has held up at 4k after the 1st one. I could probably go longer with the Trasko filter element as the motor cleans out.
Last oil analysis on the 7M was at 8k and showed minimum wear metals and a normal drop in the additives...TBN (ability of oil to neutralize acids) is holding up at half of new. There was zero water/antifreeze and < 0.2-3% insolubles and fuel...viscosity is holding in spec range. A spot test showed the oil is a dark amber (not black). In the R22, no analysis yet. At 3k a spot test showed the oil looks close to new.
The oil in the Supra is not going to make it's full potential OCI...the motor is going to get replaced soon. If the same analysis trend holds for the truck, it would not surprise me if it will go at least 12k. Keep in mind the OCIs I'm talking about include analysis...the 8k OCI with filter changes at 4k you hear me talk about is a safe interval with a "true" syn oil if you do not do analysis. With analysis, you change when the TBN drops to ~2...the oil adds you do when you change filters like I do above keeps the additives in the oil at the effective level.