Thanks for all the replies and sound info, all. Anyone know if the German Ravenol Is the only one with the 4/5 group base? Just curious who out there makes the good stuff, lol. I didn't even see where Kendall mentioned base oils. I was also wondering why I hardly ever see or read about anyone using factory oil i.e. full syn ACDelco? How does the factory oil stack up to the aftermarket stuff? Part of me does not want to trust them… My thinking is that they will put something or create some thing that is "good enough" just long enough to get you through and of warranty before things start breaking so then you have to pay for the repairs out of pocket, lol.
Go with Castrol 0W40 or Mobil1 0W40 FS.
Forget group. Focus on approvals. GM Dexos1 is far from European approvals. That engine has roots in Europe, more precisely all the way back in 1991 in Opel. What you want to go for is MB 229.5 as it is most comprehensive approval among Euro standards. However, these oils are usually very heavy W30 or light W40 oils. Any oil thta has MB229.5 approval is much "better" product than anything Dexos1 for turbo application.