Moontan,
I have a 2003 FZ1 and use the amsoil 10W-40. I have no complaints with the use of amsoil in my bike. I switched to amsoils after 1000 miles last year and then rode out to South Dakota last summer, 2200 miles total and no oil comsumption.
I would recommend using the yamalube for break in purposes and then switch to the amsoil. There are mixed opinions on the use of a synthetic oil in an engine with a thousand miles, however the opinion is that the engine is well broken in by 600 miles and the use of synthetic oil is appropriate.