Just in passing, I know some parts on the engines have to wear a little to seat, like piston rings. Sometimes the synthetic oil are too slippery for the parts to seat.
When you're dealing with an air-cooled engine, the temperatures can run to the extreme. Most V-twin air-cooled engines have different temperatures on the front and rear cylinders. Synthetic oil doesn't break down like blends or petroleum oils.
If it were me, I'd follow the owner's manual for the warranty period.
I am sure Amsoil is a good product. Personally, I have always used Royal Purple. It just a preference.
Smiles!