The other day I posted a topic about whether Havoline 5w-30 GF4 or Motorcraft 5w-30 GF4 would be better. I got some response but it got me to thinking about a related issue. The Havoline is a Grp II+ base and the Motorcraft is a Grp II / Grp III base oil. Now which if the Havoline has a supposedly lower quality base oil does it have to make it up with the adds and conversely does the supposedly superior base oil in the MC mean that they can skimp on the adds? So which is the more crucial piece, base oils or adds?