its good.... i dunno if its the best, depends on your car, I use it on my nismo right now, but im thinking of switching back to full euro synthetic which is the castrol 0w-30 green bottle, or gold bottle.
i just did and oil change for a customers of mine on his and his gfs' car. He said they notice the performance is doing alot better then regular motor oil. So i used Purple Royal on this gfs 99 Mustang and on his 89 Mercedes 300SE. yeah about $8 quart.
if you have a modified car and use it at the track/drag/drift etc. then royal purple and other oils like eneos are good for your car but if your not going to do any of that then most name brand synthetics will do.