Ah, my mistake. I would have thought if it's dark enough to capture the aurora that well, then the milky way would show up more clearly.
How many images if you stack in the second one? I guess it's probably just light pollution, even if you shoot from a low light polluted area, if the camera is aimed in a direction where there is some glow it can wash out some detail and colour. As for noise, I don't know how well the 70D handles it? I know my 60D is pretty bad at 1600 and pretty unusable at 3200. For astro I always use my Canon EOS M as it very usable at 1600 and not too bad at 3200.
Also, what time are you shooting at? Being up in Scotland you're probably only getting a couple of hours of truly dark hours during the summer. Even here in Sheffield it doesn't stay properly dark that long.
In the second one I had 5 or 6 images for the panorama. I have read image stacking can help but not tried it with milky way shots. That number of shots may have been a bit over the top but I have found stitching photos of the milky way to be a pain so far. I do have enough images to do a 360 panorama of the aurora but it is not working out how I would have liked. May be down to me and how I am stitching it in Hugin/LR.
At 1600 I think it is usable but other more experienced folks may disagree.....certainly it is better than my old 400D which was terrible at ISO 800.
In my second set of images these were shot around 1 - 2am, which is still within the darkest hour according to the Clear Outside website. The shot with the aurora was taken a bit later and I think twilight was starting to come in behind me so may be the reason it is washed out. The aurora that night was very active and even showed some colour to the naked eye so and lasted well into the early hours.
...).
