I gave up using my 40D in poor light, it's not a good performer. Anything 800 and up is pretty bad, which sucks. For low light action, forget it. Then again it shouldn't really be that much of a surprise, it uses the same sensor as the XTi for the most part.
If you want dirty pics it's great. I crank it up to 2300 and fire away, shut all the NR off. :thumbup:
Noise is an FOL with digital photography, cropped sensors plus a high MP count just doesn't workout, never will.
I picked up a 50D the other day. While I like the camera initially it's worse at the high range than the 40D. What I've been finding out is it's lens picky, certain lenses will give you great low light high speed images, while other won't. I won't give up on it just yet. If it can't perform in low light the way I'm needing it to I might make a switch to the D300 which I've seen is capable of doing some things the 50D can't.