Oil will ALWAYS be a controversial battle between OPINIONS..
Royal Purple is something I will forever stay away from.. I have seen 2 engines and roughly 3 automatic transmissions blow (which appeared to be prematurely) while using Royal Purple.
Coincidence I would like to think so but it stacks the books in royal purples fault in my book.
I don't buy much US spec products (parts, oils, other fluids, filters etc) I stick with proucts I have tested for myself..
As for engine oil I use ELF 5w40 Basestock 5 synthetic oil.
This stuff is made in France (the europeans have such better standards then the US market does) and I have used it in 3 race engines, 4 daily drivers, and most of my team uses it as well.
The other advantage for myself is that I sell the product so I get it at a reduced price.
One thing I learned over the years is that in the USA in order to write "synthetic" on an oil bottle the company ONLY has to put 18% synthetic oil in the bottle and the rest can be non synthetic oil.
Mobil 1 and Castrol are both partakers in this cheating war. I have had test samples of Mobil 1 engine oil sent out.. on a 10w30 engine oil after running the car for 2000 miles the oil sheer was down to a 0w20 and the conclusion was that there was only 21% synthetic polymers in the oil (new out of the bottle). This makes me wonder why it is that I am paying for synthetic oil and only getting snake oil..
I also am a firm believer that if you are looking for the best highest quality oil there is.. u can't buy it at Walmart.
A few oils I would highly recommend
Synthetic:
ELF (in the states though known under the parent name "total")
Nippon
Non synthetic oil:
Mobil clean
Castrol GTX
Valvoline
anything else IMO does not measure up and also seems to be more of a hurt in the pocket for what you are getting.