I've no experience with Royal Purple but I can tell you from personal experience on my vehicle and those that servoce in my shop that Amsoil lubrication products are
amazing. From the performance on my SUV (Isuzu Rodeo)
to my customers feedback after converting over to Amsoil
have all been favorable. After going 17,000 miles with Amsoil Signature Series oil with an Absolute Efficiency
oil filter,(98.7% @ 15 microns compared to 40 to 80% in conventional filters),and refilling with same, I was amazed that for 2 weeks the oil still looked like new oil.
Where my fuel economy would vary by 2 mpg hi or low, it stabilized right at 21mpg.
all that said, as a in the field professional with 34 years of Automotive repair experience, I have no issue with continuing with these drain intervals in an ongoing basis.