did the prop spin test yesterday, had one with the the old 80-90 Amsoil and one with the new 75/80-90 Amsoil the diff is the old you might be able get 1 revolution ,with the new you can get almost 3 revs ,i know it's a little thinner but still seems to work as good as the thicker lube. :

i am an amsoil dealer, i only use torco in my personal drives very expensive but it is horsepower. i would only use amsoil or merc hpf in a pinch