40D is a great DSLR for Astro imaging - the LiveView function makes focusing easy, and the supplied EOS utility software allows the automated operation of the camera for setting up a sequence of remote timed exposures - eg 5x60 second exposures, press start and back away slowly!!
Noise reduction is great as is the colour of images coming straight out of the camera.
Please take a look at the link in my signature below to see what I have done with this camera.
I'm considering modding the 40D also, but have to say I've been very happy with it out of the box for astro and daytime work
All the best with your choice.
If you're considering a modded camera, check out some of the cameras Eric (ezystyles) has for sale on IIS and at his own web page - cheaper than new 40D