I saw lots of anecdotes; if there were data, I must have missed them, though not for lack of looking.
RobertC, I'll agree with you that the 'accuracy window' (what us old lab-rats call 'test precision') is generally pretty tight for bench tests (viscosity, TAN, TBN, ICP, etc.) But an engine test stand is a whole different animal. They are run with, well, engines. So you have to start with the much greater variability that comes with using a commercial engine as your 'instrument'. Then you have to multiply that variability by that of the bench test used to evaluate the end-of-test oil. The reason bench test variability is so tight is because they well-controlled, highly isolated simulations of mechanical phenomena. Engine tests tend to sprawl.
I base my opinions on 35 years in laboratories located in various corners of the lube business. These have included analytical testing, product development, release testing and field tech service. But in the absence of that, I'd take the advice of an uncle over a fast-talking sales guy who stands to make a (potentially excessive) profit on my decision.
The notion that buying a synthetic from a compounder-blender is somehow sticking it to 'Big Oil' is the second funniest thing I've heard today, right behind the Korean techno-pop singer doing to Japanese roach-spray commercial. Where to you think those compounder-blenders get their molecules (and often their formulations)? The PAOs are probably coming from ExxonMobil, or some other major with excess capacity. Mineral base oils also probably from ExxonMobil, maybe Shell? (Who has surplus these days?) Addiitves will come from Lubrizol, Ethyl (no mom & pop shops, those), Oronite (Chevron), Infineum (ExxonMobil - Shell), or a few other players that may look small until you figure out who owns them.