The bottom line on Oil may be found here:
Ceck the forums and get ready to learn.
Basically oil should be changed before it wears out. How do you know when that is? Used Oil Analysis UOA.
If you change every 3000 miles and use anything more than the least expensive API service rated Dino oil then you may be wasting money.
True synthetics can go 15000 miles in SOME cases, with filter changes along the way, read about it.
Filters are very important, Fram doesn't measure up to the standard you want generally. Which ones do? Actually quite a few. WIX,Champion, Pure One etc.
I tore down a 67 GTO 400 engine with 70,000 miles on it and it looked new, even the cross hatching on the cylinder walls was visible. Oil was quaker State 10W40 every 5000 or so.