Base stock matters, but it's always important to remember how much you (and all of us) don't know... the same could be said for all things in life. All PAO, ester, Group III, GTL, AN, etc. base stock is not created equal, there are many types of each (some better, some worse, depending on application). This is evident in some of Mobil 1's group III based-oils that have the specs of a group IV/V based oil. I lean on the side of sticking with huge multi-billion dollar oil companies (Shell, XOM, BP) with R&D budgets the size of smaller engine oil companies (at least for my DDs, racing oil is a different story). Remember there is a ton that goes into oil outside of base-stock and zinc/phosphorous/moly/calcium/etc, and we have no way of knowing the qualities of those other ingredients.