Is it possible better base stock probably don't require as high a VI to perform? VI is not the be all and end all.
PU is superior to PP in every way.
That question indicates not a full understanding of the ramifications of viscosity index.
Generally the higher the VI of a base oil the higher it's quality. That's the main difference between a GP I, GP II and synthetic GP III oils.
With regard to the VI of finished oils.
You cannot discuss properly an oil's operational viscosity in an engine without referencing it's VI, it's that important.
Since most vehicles operate their engines with oil temp's that vary from cold (thick oil) on start-up to hot (thin oil) when operated under continuous WOT conditions, a higher VI oil will provide the benefits of being both lighter on start-up and well as providing greater high temp' protection at higher than normal operating temp's.
So yes in terms of viscosity, for most applications, from one's daily driver to a race engine, VI is "the be all and end all".
That said, there are many other secondary but still important attributes that make up an motor oil. Deciding what off the shelf motor is best for any application often involves choices that that are compromises.
Is "PU superior to PP in every way"? Absolutely not.
PP grades have been formulated with a lower viscosity than PU, consequently if you're main interest is a lighter oil then PP may be a better choice. What are you giving up? PU claims to clean a bit better than PP. PU may also be less volatile in service. Does PP perform poorly in those areas? No, in fact it performs well above average compared to it's competitors.
The bottom line is, the more you know about a product the better a choice you'll make.
One final comment on VI's importance in motor oil. It is the OEMs that are the main drivers of the development of higher VI oils. If the OEM oil spec'd for your vehicle is a high VI oil, I'd think twice on what you're giving up if you want to use a lower VI after market oil.
