I am no petrochemical engineer, but this is the best of my understanding.
Synthetics (today) are more stable at higher temps and can be better produced to protect against the forces in an engine. But 'Synthetics' is a broad term - as is the the term 'Mineral'.
There are 3 base types of synthetic stocks - PAO, Di-ester, and polyester. Mineral oils us a mineral base, synthetic blends use a mineral base as well. They all differ in the additive packages used in the base.
The best indicator of wear and protection I know of, is the Falex 'pin and block' test and the '4 ball wear' tests. You can generally find these results on the web for many oils.
For me, there are two basic ways to determine if one oil is more 'slippery' than another.
1- Dyno testing and track testing. An oil that is more slippery should produce more power and improve times on the track due to the reduced friction robbing less power from the engine and drivetrain.
2- Coast down testing. On a flat piece of road or track, an oil that is more slippery will allow a vehicle to coast farther when compression braking or when the clutch is held in.
I use an a very accurate accelerometer for both tests.
I regularly see results for synthetic oils that indicate that the better ones are significantly more slippery than mineral oils, that they protect better, and last longer.
One side note, synthetic additive packages tend to use very large molecular chains. There are some aftermarket oil filters that filter too well, and can remove the additives from the oils - not a good thing.
