Been running synthetic ever since Mobil came out with Mobil 1 back in the 1970s. When I read about them putting a over 100,000 miles on a Cadillac engine, tearing the engine down and micro-metering all the internal moving parts, and finding them all in like new measurements, I could not go any other route. You can find that article in the old 1970 Popular Mechanics magazine. Very impressive. I even use it in the zero turn mower and the snow blower.
And then the dw's uncle was the long time head mechanic for for a major regional ltl trucking company. They tested some synthetic motor oil for a unnamed oil refinery. The ran the one in one diesel only, put over a million miles on the oil. Did nothing but change oil filters ar the specified time and top of the oil. No special filters or anything. That engine was tore down and micro-measured twice and all the parts checked out with like new measurements. They kept running the tractor as a city tractor and yard tractor after it made the million mile mark.