The consensus on Royal Purple in the oil elitist forums is that it's decent oil, just overpriced for the level of protection it provides. Not many people other than fist pounders will definitively tell you which oil is best to use in your particular engine because of the myriad of different applications and usages, not to mention the legal implications if they tell you wrong.
All I can tell you is that I do not recommend Rotella-T 15w-40 as I have personally seen wiped cam lobes on break-in. I'm steering away from conventional oils in the past few years even though I have thought for years that "oil is oil" as long as you change it often. Synthetic oils have much more stable cold properties which matter more on initial startup, as well as better high temperature properties if you would happen to lean on the engine or heaven forbid it would overheat on you. Seems that oil companies are not really spending the time on their conventional oil formulations, but rather putting the brunt of their testing and research into their synthetic brands. For the limited frequency that I drive my classic vehicles, I sometimes go a year or two between oil changes. Even with the maintenance habits associated with that duration, using synthetic oils have shown me no ill effects as to their prolonged stability over such a long period of time.
I have been running some of the new Pennzoil products because of their new technology, availability and competitive price. My old 66 F-100 responded well to the Pennzoil High mileage version to where I noticed an improvement in the way it ran. I use their Platimum synthetic version in my 2012 Mustang GT and my wife's 04 Freestar minivan. Both with good results.
I believe all of us on this site want to run the best products available in our vehicles, but ultimately I believe we need to have more information about what we are dumping into our engine so we can back up our claims. I suggest you take some time and review the data in this web blog. It is a substantial read but answers a lot of questions that discerning enthusiasts care about in regards to engine oil selection in our cars.
https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/
The Valvoline VR-1 oils are near the top of the chart on that blog for wear protection. If you are happy with how it performs and it's available and in your price range, I suggest that you keep using it.
