Oil questions tend to be Very subjective. My N1K will be switched to full synthetic at around 4 to 5K. I work in parts at a large dealership, Yamaha, Honda, Polaris & Ducati & that's the same advice I use to customers with their machines. The protection additives in syn oils are such to allow up to 5k between changes without engine issues. These are my beliefs & I'm sure there will be different opinions & brand recomendations. Unless you're having any issues which need warrnty attention, I do my own first service. Service manuals are your friends & Kawasaki manual is relatively inexpensive.