I found this very interesting article comparing motorcycle oils to car oils. Read it and lets hear everyone's thoughts on it. Personally I still use regular Castrol GTX 20W-50 in my air cooled BMW R1100S and it runs great. I change the oil every 3K miles with the filter and I'm good to go. Anyway here's the link:
http://www.ibmwr.org/otech/oilreport.html#chartc
http://www.ibmwr.org/otech/oilreport.html#chartc