Here's Chevron's marketing blurb about their GR-II base oils: "Compared to Group I base oils, ChevronTexaco Group II base oils significantly reduce additive requirements, due to higher purity and oxidation stability. ChevronTexaco Group II base oils provide higher VI, lower CCS viscosity, and lower volatility."
One of the engine makers' needs with the latest oil spec, API-SL is for the oil to be good for a longer drain interval. The car makers had been seeing added warranty costs from car lessees who'd turn their cars back in after the three years, had done very few oil changes, and the car makers re-sold these as "certified" used cars with additional factory warranties. Oil suitable for longer drain intervals would lessen engine damage in these cases and save the car companies money.
Ken