Lester, it was indeed. It's a bit frustrating not getting the H-alpha signal, but I mainly use the camera for family portraits so I won't be modding it.
Check out this image for an example of the 5DmkII's native ISO 6400 performance... I think you're going to enjoy it!
If the weather behaves this weekend, I might try to intentionally image this dark thingo (lack of a better name for now).