Just because your engine does not have valvetrain noise at startup does not mean it is running better it just means that the RP that you are using is a bit thinner than your older oil at startup, thin enough not to make the valve train clatter. I will play devil's advocate also and say that if switching oil made your engine run that much better something is not right with your engine. Can an oil make an engine run quieter? Sure. Now does that mean it is running better? That is arguable, some engine noises are harmless especially ones that go away a few minutes after start up.