I did a dyno test a while back with a 78 Camaro I had with a zz4, HOT cam, air gap and Ede 750. Ran 10W-30 Valvoline VR1 on the dyno, 3 runs to establish an average. Changed to RP 10W-30 XPR, drove the car about 60 miles and made 3 more dyno runs. Gained an average of 13 HP and as much TQ.
If an independent study is done with about 4 or 5 different oil brands I would probably believe them. A test done by ANY company testing their product against another is telegraphing the results. PLUS, the oil they pick on is the one they're afraid of.