A test done here many years showed a lot of expensive brand name oils...failed. This was just one test, known as the Timken OK load rating test. A roller is held in place, immersed in oil, & a rotating load placed against the roller. The roller becomes damaged after a while. The length of the scar on the roller & the force reqd to produce it are measured. Some semi syn oils outperformed their syn cousins!! Mobil 1 did worse than Mobil semi syn. Other poor performers were Shell Helix, Gulf Western, Fuchs, Motul, Elf, Castrol R syn, Red Line, Penrite HPR.
Oils that did better: Pennzoil GT, Valvoline Duroblend.
Equal first place was Penrite syn & Royal Purple R51.