Let me add here that I have used Automotive Synthetic oil in my motorcycles now for over 15 years with zero, REPEAT
ZERO problems. No clutch problems (and I abuse my clutches when drag racing) no engine problems, and no transmission problems.
Yes, I've read the analysis data that shows that there are different additives in Motorcycle specific motor oil than Auto specific motor oil, but that same study also showed no difference in performance. The chemist who ran the test was baffled by why they should formulate the oils differently. The different additives didn't seem to have any reason for being in the oil.
I'm sure there will be heated debate about this, but my experience speaks for itself. I've used Castrol Syntech for many years, and have switched to Mobil 1 Extended Performance 15-50 about a year ago.
Here is a great article from Motorcycle Consumer News that should help you decide what is right for you. Yes, it's old (1994) but it's still relevant.
http://www.xs11.com/stories/mcnoil94.htm