believe it or not, that image is a JPG straight off the camera! no calibration or anything!
it's a lot easier to get an impressive image on a bright object working at f3.3 but from what i've seen there's not that much difference between the last few Canon SLRs.
i really don't think the ISO setting makes that much difference above say ISO400. either you amplify the signal and noise in the camera with a higher ISO or you do it in software starting with a lower ISO. you're at unity gain by about 800 and even a little bit less makes bugger all difference.. eg in this test:
http://philhart.com/content/astropho...xposure-length
can you try something similar with your camera (just varying ISO) and see a bigger difference?
the 20D is a good camera.. big pixels.. but i can't explain why you're seeing a bigger difference than i would expect?
Phil