I used Rotella in my 625 smc with no problems. In my '09 690 Duke I used Spectro 10/50 semi-synthetic with no problems and Motul in my two-strokes. As stated before... stay on top of your oil changes and you shouldn't have any problems. I spoke with a race bike engine builder at one of my local shops and he preferred semi-synthetics to full synthetics. He demonstrated that you can feel the difference in lubricity, is that a word, when you rub it between your fingers. The semi did feel slicker than the full synthetic. He said to change the oil a little more often. Also, he said to stay away from Royal Purple. He said every race engine he built which used Royal Purple, didn't last long. Once he stopped using Royal Purple, the engines ran better and lasted longer. That was five years ago. Maybe Royal Purple has gotten better. I don't know, never used the stuff. I'll have to try the Motul ester based, or go back to Rotella if they make a 10/50. Lately, all I've seen is 10/40 or 20/40.