I know a little about oil. After thirty plus years of driving one observation is that after about 5,000 miles the oil is dead. There's little lubricity in it as you rub it between your fingers compared with new oil. You can literally feel the renewed pep in the engine right after an oil change. I've noticed this with conventional oils and synthetic oils in mostly the 10W30 and 5W30 range in my lifetime.
My Gen IV 5.3 and 6.2 LS engines likes their oil changed at around 4,000 miles.
Anyone ever see the movie, "The Super" with Joe Pesci? His slumlord father had a motto that when they bought a real estate property they did nothing with it. My father applies this to his cars for some reason. Back in the early '90s he didn't change the oil in his '80 Delta 88 and the motor quick working after 34K miles since the last oil change. My brother and I saved that engine by pouring lots of gasoline into the crankcase. Then the other day my folks called me from the side of the road, Dad ran the little Kia out of oil again. He could not even remember the last time he changed the oil, said the little sticker fell off the windshield a year or so ago! Lucky for them, he added two quarts and the car started back up and got them home.
I guess Dad's treatment of his cars makes me pay more mind to my own. Well, I'm a "car guy" and he's not, I guess that plays a part in the thinking too.