To quote from _The Wonderland Gambit_ by Jack Chalker: "Everything you think you know is wrong".
In this context I am speaking of the new GF-4 formulations of what we think of as well known popular conventional oils. I don't think that any of us here have any basis to comment on the relative superiority of Mobil Drive Clean, Castrol GTX, Motorcraft, etc. etc. etc. in their new GF-4 forumulation because we really don't know how much has changed. Perhaps some of these oils went through major reformulations to meet GF-4 specs and some others may have required little or no change from the GF-3 generation.
In my view, all previous data and biases are pretty much worthless now until we get a body information on the new stuff.
I would also speculate that within manufacturers we are going to see even less actual differentiation between formulations of their various labels then we have in the past. ConocoPhilips, for example, has all but stated that their Kendall, 76, Conoco and Phillips 66 brands are all the same stuff with different labels.
John