ive done a lot of research on this and am the person that started the other thread oil help. the more you read the more you get confused. anyway it matters what temperature you start your bike up.
1 rotella is great stuff and the cheapest. me personally i wouldnt use it because it doesnt have corrosion protection not because its made for diesls or that its 5w40 that only matters for cold weather starting. if you go with rotella make sure its the full synthetic.
2 manual says 15w50 shell which you cant get in the states but you can get motul 300v 15w50 full synthetic but its 16 bucks a qt plus shipping.
3 my stealership uses motorex 10w50 thats 18 bucks a qt.
4 the other stealership thats near me uses 10w40.
5 spoke to ducati na in California they recommend 10w40.
all that being said i went with amsoil 10w40 and i can get it for about 10 bucks a qt. i went with this because a gallon would be 40 bucks. the rotella is 27 so i can justify the extra money. I dont believe the motul is 6 bucks a quart better then the amsoil and i dont believe motorex is 2 bucks a qt better then motul.
also for the same price as castrol rs racing 4t 10w40 or 10w50(castrol makes both) or mobil1 10w40 both for motorcycles are the same price as amsoil and i just believe amsoil is better for the same price
hope that helps