Forgive me if this has been asked before. I've been researching the best oil to use in my 1.6 liter gdi turbo. The manufacturer recommends 5w40, but you can use 5W30 for better fuel economy. I know that GDI motors are known for carbon buildup. I see that there is a SN plus rating that is supposed to help with that, but it seems that is only available in 5W30. Is it worth going down to 5W30 to get the SN plus?