M 31 Andromeda

Objects with such a high dynamic range need to be captured with different exposure times and then stacked in DSS using the wide dynamic range mode. In your case, instead of 150 frames at 5 minutes each, you could try 50 frames at 40 seconds, 50 at 120 seconds, and 50 at 300 seconds. That way, the center won't be overexposed and the periphery will show up well. I haven't tried this myself yet—haven't had the chance (or weather) for it.