As a base oil - PAO allows: - more additive chemistry, as PAO has less SAPS compounds in its composition. SAPS kills modern 3 way catalysts or diesel DPFs and has stringent limits on its presence in oil. SAPS also should be bad for DI engines due to providing the compounds needed for valve deposits(Gokhan may disagree). I havent seen tests / studies to the contrary. More moly or ZDDP can be added to PAO oils having the same or lower total SAPS content. - more oxidation stability, requiring less antioxidants for similar intervals / use - oil can contain friction reducing / extreme pressure performance additives, rather than just antioxidants. Would also withstand nitration from fuel contamination better. - less VI's are needed to achieve low temperature performance/winter grades. VI's can leave deposits or degrade and let oil slip out of grade. - better NOACK - depends on other parameters, but I believe, a well established fact. Lower NOACK also helps control intake valve deposits and oil consumption. Most oils use PAO and other groups. Either way PAO is engineered to be better and uses pure chemicals as its building blocks. Yes, Group III can make a good oil,its just that Group IV is better.