I'm going to try again tonight to get a star shot, but this one went too long and the sensor got noisy. Maybe I'll try a lower ISO, for sure I'll do it for less than 55 minutes. A spot without as much ambient light would help as well.
I was pretty surprised to see how much noise I got on a 5D at 55 minutes (ISO 320) when running cf-long exposure noise reduction. Maybe ISO 200, f/5.6, 35 minutes... thoughts?