AMSOIL did a lot of research recently, on oils.
Some expensive ones were a joke performance wise.
part of their tests were done over 400,000 MILES in a semi(artic), and showed wear to be within NEW tolerances.
They also tested taxis, over a two year period, some other owners reported up to 5mpg better.
The test really was independant, and over years with different cars trucks buses etc, so pretty much all variables.
One thing that did come to light was needless waste of oil being changed too early, they went on to recommend every 25,000 MILES between changes.
tabetha