After a ton of research, and testing in my engines, I settled on Amsoil 20-50. It improved performance and mileage on my motorcycles, and I run it exclusively. Yeah it is sold only under railroad bridges by leprechauns, but from the second you put the stuff in, you can tell a difference. No I don't sell it, but I do strongly recommend it.
Wild Bill
BMW GS1200, Buell XB12X, Buell XB12XT, Star Roadliner S