I'm not sure what's up with those aurora shots. Both just look wrong to me for some reason, even the ISO800 one, I can't explain it.In the ISO 800 shot, I see the stars are leaving a very slight trail, so that they appear a bit teardrop-shaped (motion diagonally, between a 10-11 o'clock position to a 4-5 o'clock one, roughly). This is likely due to some camera movement (at a wide lens setting, and only 8 seconds, there is not enough time for the rotation of the earth to become visible, I would think...maybe I could play with the Stellarium planetarium software a bit to figure out for sure).
There also appears to be some "chunkiness" or blurring in some subjects, and the blue sky near the waterline appears to have chroma noise blotches.
The tiger picture surprises me a bit for two reasons - one, it doesn't seem as "sharp" as I would have expected from that lens. The shadow areas (the dark greens, at least) appear very good though, much better than I would expect to get at 3200 from my 7D for sure.