The subject of engine break-in is argued as much as the subject of which oil to use.
Honestly, everyone is right. As long as you use an oil, you won't hurt anything. As long as you drive the damn car, get it up to proper operating temperatures, you are doing it good.
What happens at the factory is engine
RUN-IN a term which is often forgotten.
The belief that the engine is
BROKEN-IN at the factory is a misleading one.
During
RUN-IN, the manufacturer is only assuring the engine doesn't leak, meets their specs, and most importantly setting it up for the ultimate BREAK-IN by the user.
During the Run-in, there is inherent metal to metal and wear occurring. This is obvious. Some consider this Broken in. However, no matter what scenarios they develop in the test cell to replicate real world operations, they can never replicate actual real world scenarios.
In airplanes, we are told to take up to above 75% of rated engine horsepower for first 50 hours. (feels like an eternity) It is the scariest 50 hours for the pilot.
If we apply that convention to modern, liquid cooled automotive engines, we can probably accomplish the same thing.
So for a 350HP Nismo, 75% works out to 263HP. For argument sake, if we develop 350@7500rpm, 263HP would be around 5600RPM. Not too far off 4000.
Again, this brings back why Nissan chose 4000. (which work out to about 55%HP) Nice even number and you wont be babying nor destroying in extreme conditions.
Just a scenario, I'm not suggesting this is how it's done or actual math etc. Just my aviation scenario theorized for automotive use.