I will probably stick to 15000km OCI as this is what Volvo recommends. Of course both oils can certainly do much more than that but the problem then is the oil filter. Extending the OCI would also require a better oil filter which I don't have.
My issue with the M1 5W40 is that since it's a full synthetic, if my 200k miles engine starts to leak because sludge has been removed from seals, I will not be able to use RX to recondition the seals. The engine is supposed to be clean but... By the way, is there any evidence the TopTec oil is not 100% synthetic? LM says "The combination of unconventional basic oils using synthetic technology,
together with the latest additive technology.....". Does it mean it is semi-synthetic?
So keeping 15000km OCI, for you the price difference between LM and M1 oil would justify the move to M1 5W40 then?