That's a beauty!! Gotta be proud of that process
The random banding with the 40D appears to be common problem with them all.
More noticeable with sudden fades in bright to dark areas; and during high temps.
Unfortunately I could never get rid of it, even with darks; as the banding seems to randomly flow through the image. You can see this more noticeably when viewing stacking flows in CCDStack; or timelapsed photos(avi movies).