Using Mobil 1 5W-20 in my SEL V-6. I have been a satisfied Mobil 1 customer for many years.
My understanding of oil behavior in an internal combustion engine is that there is mechanical "shearing" of the long molecules of oil during normal engine operation. Non-synthetic oils are more prone to this damage because of the long-chain molecules used to provide the proper viscosity to the oil. Over time the oil loses viscosity and does not provide the equivalent "film strength" under high heat. As this viscosity degrades, the ability of the oil to provide a film between reciprocating metal pieces is reduced, allowing wear.
Synthetic oil maintains its film stength under heat far better, and is less subject to mechanical damage from the engine internals.
But the real million dollar question is the oil change interval. The more often the oil is changed, the less the oil deteriorates when it is in the engine. So if you change your oil every 3000 miles, non-synthetic is probably no different in engine wear than synthetic.
Having said that, I still use Mobil 1 because I feel better about it.