I believe that if the mineral based lubricants were matched to the ambient temperatures throught the testing, there would be very little if any measuerable wear difference between the engines.
Typically synthetic engine oils have the advantage of being the right viscosity for the job over a broader temperature spectrum than mineral based lubricants.
Winter will be at our door steps in a couple of months in northern USA and Canada.
At the moment I have straight weight mineral oils in a few vehicles, some of which don't belong to me.
I feel that as long as day time temperatures remain high, today over 95F, and trips are long, an SAE 40 is ok to use and MAY provide better wear protection than a multi-grade engine oil whether it is a synthetic lubricant or not.
BUT....All it takes is a few cold nights, and suddenly I have the wrong viscosity of oil.
The other end of the temperature spectrum is in mid winter when the temperature is at -40C instead of +40C.
At this extreme cold, a mineral 5W20 or a very good 10W may perform just as well as a 5W30 or 0W30 synthetic.
I doubt at this cold temperature the engine oil ever properly warms up, even on the highway, to the point the engine is wanting for a thicker oil.
Now I doubt if any oil company is going to start testing this theory on private passenger vehicles and risk killing off the lucritive synthetic engine oil market.
And I doubt if any one person is going to purchase two identical vehicles with twins driving them.
And, I doubt if many people would want to change out the mineral oil 6 times throught the year to optimise the viscosity to the ambient temperature, while the vehicle using a synthetic 0W40 can use the same oil all year round.
So we are back to square one.
I'll monkey with straight weight mineral engine oils, and perhaps a 0W40, or 0W30 for a few months, while you laugh and sit there with one multi-grade synthetic all year round.
The difference is....I'm paying $2.70 CDN a litre, and you are paying through the nose.
It all boils down to how many miles you put on your vehicle, and how much you want to pay to lubricate the engine over the same service life?