I can not find the reference at this time but a Noack rating of 11.0 is the max that should be used in a GM, and probably all, DI engines. 10W30 will tend to have lower Noack numbers then 5W30. Typically a slight difference.
To the question, “what the NOACK Volatility means and why it's important”. In a non DI engine the gas passing over the intake valves helps keep them clean and aids in “washing off” vaporized oil. In a DI engine fuel does not pass over the intake valves and thus vaporized oil will deposit on the valves. There is a pic somewhere on BITOG of a VW / Audi DI head after 7X,ooo miles and the valves are caked with deposits. If not corrected this will lead to messing up the valve seats as well as the valves.
To the question, “what the NOACK Volatility means and why it's important”. In a non DI engine the gas passing over the intake valves helps keep them clean and aids in “washing off” vaporized oil. In a DI engine fuel does not pass over the intake valves and thus vaporized oil will deposit on the valves. There is a pic somewhere on BITOG of a VW / Audi DI head after 7X,ooo miles and the valves are caked with deposits. If not corrected this will lead to messing up the valve seats as well as the valves.