All right, her comes my opinion piece on Amsoil. I have used Valvoline synthetic in two GMC trucks and both now have 100,000+ miles, no problems. I like synthetic, I will continue to use synthetic. I am currently breaking in a new 2012 Vulcan Voyager, last week I rode 200 miles around Daytona and the dash MPG was 34.2. MPG has been creeping up during break in. I did the 600 mile oil change and for the first time used Amsoil synthetic 10w-40. Today I did nearly the identical ride to Cocoa Beach, on the way mileage was 34.2 on the way back it was 34.4 MPG. I have been told many tall tales about Amsoil over the years and decided to test it myself, no big jump in mileage, no big change in shifting or acceleration. I really didn't think there would be. Do I think Amsoil is a premium synthetic? Yes. Will I continue to use it in this bike? Yes. Have I become a member of the Amsoil Zombie Cult? No.