Harry,
FYI, Royal Purple and Mobil One were the worst oils I experienced in my car (06 Civic SI, 2.0 liter engine). I understand what Buster is saying, but it's hard to say it's psychological or that the oil "needs to lay down it's protective barrier" as the cause for our observations, when an oil switch resulted in almost immediate tangible differences in operating character. My engine sounded harsh with Royal Purple, it didn't rev-happy with M1. The engine worked great with Pennzoil Platinum, even Supertech 5w30, and now AMSOIL Series 2000 and SSO. Sure, you can say it's psychological, but I didn't use those oils back to back and both exhibited easy-to-discern engine differences.
On the same note, I always ran 5w30 in my wife's Saturn Ion. In it's last oil change, I switched to Rotella 5w40. It became the smoothest the engine has ever run, bar none (not a smooth engine, so lots of room for improvement).
Joe