Synthetic oils

First off I never run the synthetics in my muscle cars, I change the oil to often because they sit a lot of the time in the garage and moisture is a killer. I do run Mobil 1 in all my day to day cars (after the first 5,000 km from new) and have since 1979. I put whatever grade the OEM calls for, no farting around, and change it every 7-8000 kilometers mostly cuss its dirty. Years ago I sent in a sample of Mobil 1 that had over 10,000 kilometers on it for analysis and the tests came back that other than being dirty the oil was good as new. In other words the package was still working, no breakdown of the oil, acidity levels were normal and the viscosity was still good.
A couple months ago I pulled the tappet covers off my 3.8 supercharged V6 pontiac engine to change gaskets. I expected that the undersides would be clean and they were spotless, no gunge, no oil breakdown. The engines got 160,000 KM on it and I'll guarantee ya that the bottom end of the engine is just as clean. The main reason I run sythetics is that at minus 25 degC, when my wife forgots to plug in the block heater, the engines starts and you've got oil pressure immediately. This stuff, 10W-30, still pours at minus 40 degC whereas conventional 10W30 is paving tar at -40.