Is Amsoil or Royal Purple any better than Mobil 1 Extended?

VERY MUCH SO

Yes, Amsoil has better test results than Mobil-1 Extended Performance: http://www.amsoil.com/lit/g1971.pdf

As far as Royal Purple goes you can contact their technical services department and ask for their test results like 4-ball wear, high temp/high shear viscosity, TBN and compare them to Amsoil's numbers. You can refer to the ASTM test numbers in the above link-- they are standard industry tests of motor oil. Amsoil's data driven comparisons don't lie.

I know your question is about motor oil, but here is a link to detailed tests of automotive gear oils that includes Royal Purple and many others including GM factory fill. Great info here: http://www.amsoil.com/lit/g2457.pdf

Feel free to check out my Amsoil website for more info, or to drop me a line: http://www.number1synthetic.com/

Good luck!

Royal Purple is possibly the best oil ever. It's the only thing I ever put in my Cosworth. It's the oil of the NHRA, which says something. In fact, I have a friend who works on gas pumps (natural gas) for texaco, and the only oil they'll use is RP and for Texaco to use a product that they don't own says something about it.