Amsoil is advertising that thier recommended oil change interval is up to twice the manufacturer interval, So if HD says change at 5K then this would give you 10K on Amsoil cutting the cost in half to about 6bucks a quart, and if this is proven, I would say Amsoil is a superior synthetic. Has anyone tried this or anything close to that mileage, a blackstone oil analysis would be helpful here.
I just think about the reasons we change our oil and to just name a few, contaminates, break down, oxidation, and loss of viscosity so if Amsoil tested well in its ability to control these variables it should be used for a longer period. I am just curious to see how it would look on a blackstone paper after 8K miles or so.
I do not doubt that the oil will not break down for 10K, but one of the things that oil does is that it's holds the engine contaminates that are drained out during an oil change. I would not the contaminates suspended in my oil for 10K.