Very good. What car btw?
Do you often encounter traffic jams and are you an aggressive driver who likes to rev harder?

Hmm maybe I'll give it a try sometime later but I doubt it'll come as clean as yours. Now is already about 9k km so normally I'd change at 10k.

I don't think automotive experts are still suggesting that.

I agree, still too much guessing here. I'd just rather follow the normal recommended OIC for my car which is 10k km using FS oil and be done with it. It's easy to remember some more, rather than every time try to extend but no peace of mind, plus the km extension makes it falls on uneven numbers of km for OIC. Just not worth it IMHO.

What is the TBN value? Longer OCI usually is also dependent on TBN value. For example oils that claim can last for longer mileage (>15k km, some even >20k km) usually have TBN value >10 or even >11, such as Amsoil or Mobil 1.

CMIIW though.