For what this is worth, I'm going to pass on what I consider to be some very reliable info, given to me by a good friend, who is a VERY serious, professional drag racer, and a chemical engineer.
He runs it in HIS competition vehicle, and tells me that virtually ALL of his peers also run the Royal Purple.... um, even those who may be sponsored by another major oil company.
Why? Yes, it's because their engines DO make measurably more horsepower with it. This friend of mine launched into a bunch of chemical jargon I had no clue about, but we eventually got down to a concept I could understand, whereby the actual "blow by" or mist created in the engine, actually "enhances" combustion in the cylinder. Sounds pretty good, right?
Well, the rest of the story is that he claims it's only good for a day's worth of runs, and must be changed beacause the effect goes away and the lubrication properties begin to deteriorate rapidly. He recommended that I absolutely NOT run it in my Viper for the long periods of time involved with normal street driving or weekend track events. But if I wanted to trailer my Viper to a drag strip for a day..... go for it, and it could be worth as much as 4-5 extra hp in my Viper.
Again, this is third party info, but it's from a guy I trust and who "knows", and I would believe everything he tells me about drag racing. My 2 cent contribution.