Best oil for alky? Wear? Hp?

Yellow rose, as a last (15th) dyno pull on my 528, i dumped the reg oil and tried Mobile one, same vicosity. I lost 15 ft lbs of torque, and didn't have a clue why. I thought i should test it at the track too, car slowed down. Is Mobil one a class4 or 5 ayn?