Oh jeez, it's been a while since I went through my experimentation phase with this bike but I remember using (all 10W-40 viscosities unless specified differently) regular Mobil, regular Valvoline, regular Castrol GTX, Golden Spectro 4, Delvac-1 5W-40 and Amsoil. I put the regular Mobil 10W-40 in and rode it less than 3 miles and brought it back and drained it. It shifted horribly. The Amsoil and Delvac-1 worked the best and I currently have Delvac-1 in it now.
I had been changing the oil at 3000 mile intervals and after seeing how some engines are shearing the oil out of grade with gear driven cams or variable cam timing I believe I'll stick with this interval and not go farther. I don't ride a lot when the weather gets too hot down here so 3000 miles will last me the summer.