Adding my two cents:
From everything I´ve read we can now change oil at far more than 3K
miles.
We can debate how much... I would´t go too far from 7.500.
No objective data to support that. Just the fact that an engine
overhaul is so expensive that I prefer to "invest" in oil.
On the other hand I feel there is a second and perhaps as important
variable: time.
I run a very low monthly mileage. This means that making 7.5K takes me
well over one year.
In this case, again, no objective data, I change synthetic every year
or mineral every six months.
On top of low mileage I have lots of very low mileage use from cold
engine.
I´d really like to know your thougths