I am using 400D but it has only slightly worse noise performance according to Christian Buil.. (
http://www.astrosurf.org/buil/eos40d/test.htm)
5 sec is very short exposure and there is not enough light signal collected (BTW, what FL did you use? what f number?).. light pollution at your site seems to be quite horrible as well, and you used a lot of stretching obviously to bring out the image above background.. increasing the readout noise in the process (banding is visible, but IMO this will be reduced to almost nothing with 10 frames or more), surely 5 frames is not enough to reduce it sufficiently.
You will have to go out in the country....