Mobil 1, good for 6k miles?

[1965GTO]

I usually agree with everything MR 50 says. However, I think I save money by using synthetic oil. I usually look for the 5 Quart jug in the clearance aisle, but even a sale will get you one for around $18. That's $3.60 a quart. Maybe 3 times as expensive as inferior oil. So if I leave it in 3 times as long or more I save money. That is exactly what I do. One year or 12000 miles whichever comes first.