from my knowledge, royal purple does claim all that stuff bout hp and mpg's but if you look at it, it is really worth the price. you can run royal purple twice(if not a little more) the miles than you could on regular old motor oil. the same thing goes for amsoil. they are truly designed for long distance drivers. the main people who use these two types of oils are highway patrol. it would be a pain in the ass for them to change their oil every 3k miles. from my experience, if you decide to run it, be sure to drain all the old oil out. if your gonna make the swap you might as well do it right.
oh and i run wix filters all the way