Since the entire industry is heading towards di turbo, consider group 3 is better then group 4 at combating lspi. Maybe pao is better in the cold and stay in grade 0w40's, but the industry is driving formulas and nothing is bigger then the di turbo driving formulas. But since they did that a long time ago, very likely it was a cost savings move. But for people with a di turbo wh research every aspect of combating lspi with a lubrication formula, Amsoil SS is one of the few solid choices.
Some grp3+'s have pao like numbers. For example, Mobil's Visom 6 is a Grp3+ base stock with a VI of 142 and a noack of 8%. Chevron and Shell have similar high grade grp3+ base stocks.