Your OEM oil cap should say: "Mobil 1 0W-40". This was the factory fill for 05, 06, 08, 09, and 10 Vipers.
This certainly remains a good oil for street use in my opinion. For track use or hot climate use, many use Mobil 1 15W-50. Of course, there are also higher cost alternatives available as well.
There are as many preferences and debates on this subject as there are oils.