Mark, I thought you owned a 5D2. Am I confusing you? No P&S is going to get anywhere close in terms of noise and pixel-density.
The 5D2 is particularly suited to night and astro photography due to its "Long Exposure Noise Reduction" function. When you take a long exposure, LENR takes a second image for the same amount of time with the shutter closed, then the noise in the second image is subtracted from the first image. It's pretty incredible. You can set it to Auto or On in the Menu. Highly recommended, making an already good noise performance exceptional.