I have Royal Purple in one of my Procharged cars, and will be changing out to Mobil1 again on the next change. I have heard stories about RP eating away at the metals if the car is not used often, and this car is not driven that much. I don't have any documented evidence to state that what I have heard is true, but have too much in the motor to take chances. I have used M1 synthetic for years in a lot of my Mustangs, and have never had oil issues with it. Don't really know why I decided to mess with a good thing.
Mustangs and Harley, I use Mobil1 and it works great! The only one I do not use M1 in is my F350... I just use Motorcraft dino squeezin's as recommended with Powerstroke turbodiesels and have never had a problem.