i researched this topic to where i got nauseous. There are so many factors involved, where you live, how you ride, temperature etc. bobistheoilguy is a good reference google it you can literally fall asleep at your computer for a month straight with all the info.
First thing you have to do is pick a grade. I use 10w40 that is what my stealership recommends, however my other stealership used 10w50 meanwhile the manual recommends a 15w50 which the brand they dont make in the states. what to do what to do. you cant go wrong with 10w40 or 20w50 or 10w50 as long as its fully synthetic. some people swear by t6 rotella. Yes desiel synthetic. I chose to stay way from that for my own personal reasons not because its a bad oil i just wasnt comfortable becuase of lack of corrosion protection. you dont have to agree with me.
Changing the oil is also not a science. the old 3000 mi rule is out the window with these synthetics being way better than conventional oil. You have to take into account your riding style. Also do you just need to top off your oil or a full change. see what works for you
Once you chose your viscosity you have to pick a brand. there are so many i narrowed mine down to 4. Dont kill me if i didnt pick your brand but here is what i determined with my own factors. again my opinion there is no science behind this.
1st from what i read and other peoples opinion the best oil for racing in this bike is MOTUL 300v 15w50 down side is it is expensive at about 15 bucks a qt. Its green smells like bananas. If you have the oil viewer you can site when you may need a change from the change in color.
2 Motorex this oil comes highly recommended and is the oil of choice in 10w50 from my stealership. Before the duc i never heard of them. its expensive at 18 bucks a qt because of the fancy bottle. I dropped this oil because i could go Motul for 3 bucks a qt cheaper and i felt that motul was a better oil
3 Castrol power racing 4s 10w50 10w40 20w50 or Mobil one 10w 40 or 20w50. you can get this in any store but the 10w50 is hard to find. At 10 bucks a qt i did not choose this you will find out why below.
4 AMSOIL I went with this oil. you may ask why and i will tell you bang for the buck. if you look around you can get this for about 10 bucks a qt. After looking at the oils above i thought amsoil was second best to motul however i did not feel that motul was 5 dollars a qt better than amsoil. At the same price of castrol or mobil one I thought amsoil was a better product and it was a no brainier to go with amsoil. I picked the 10w40 however i may switch to 20w50 as i dont ride in cold weather.
PS If you change your oil you SHOULD CHANGE YOUR FILTER.
Hope this helped. its alot of info and there is no RIGHT ANSWER but i know that oil is one of the most import and most effective way of protecting your engine.