0w 20 cannot take prolonged heat at high speeds, you see there is a reason why you see German cars use 0w 40 as at higher speeds the oil will be able to sustain the higher temp unlike 0w 20.  The nissans cylinder wall is 0.2 mm through some diamond and mold coating similar to the GTR hence would only make sense that they use 20. However 20 is not meant for very high temp for prolonged period hence why it would wear faster. Else why do you see the service intervals significantly lower then turbo Germans?

7.5k mileage 6 months for the Almera. Other makes is 10k mileage.

But interesting point to note is most professional mechanics say that mileage interval from manufacture is stretched and optimal normally is 60-70 pc of the recommended interval. This holds true cause like a certain German make sayGB oil is lifetime but ZF say every 80k km.