Actually,your right, my canon 6d can do 6400, however I was thinking of a new moon and getting the Milky Way.
I have a Nikon D4 which is pretty good at high ISO. The problem is that when you shoot the moon is that the damn moon is so bright and the sky is black. You really need to spot the moon to get the right exposure, and then work around it. It’s a good tripods and some multiple exposure stuff, you can make a sweet composite.
Getting good night shots is not something you are going to walk out tomorrow night and get the first time out.