Somehow, Rotella and other 15w-40 diesel oils have become the standard for motorcycles.. Shifting is better, and I've never heard anyone have an issue with clutch slippage..
I've been running it in my KLR for the past 15k miles, and in my Goldwing since it's first oil change, as well as my BMW (dry clutch).
Almost every Wing rider I know (both personally and internet) run this oil, and the majority of motorcycle riders I know run it, too. I also ran it in my V Strom..
I don't have my manual handy, but 20w-50 is only recommended for the hottest temps, and if I remember correctly, the recommended oil for general use is 10w-40..
Not starting an oil war, here..
While checking I found this site.. http://germz.org/klr650/oil.html
and I chuckled when his first paragraph about oil is:
Cutting to the chase: The best oil that I have found is Shell Rotella T 15-40 Heavy Duty commercial diesel oil.
I guess it's just good stuff!!