You'll need to consider what lenses you already own that will work on a full frame body & / or whether you're focal length limited & need the extra reach a crop body gives. From experience I can say that the 7D has an excellent AF system for sports, plus a great FPS rate too. From what I've read (and I haven't dug deep) the 6D will have an AF system similar in speed to your 40D but noticibly better in low light. Wildlife shooters like the extra reach of the crop, sports shooters like it's AF system and I think landscape shooters prefer full frame. .
Thank you. I really appreciate the input. Most of my work is landscape (that's why I like the HDR), and I really like shooting at night (cityscapes fascinate me at night). Think the 6D is going to be the way to go. I think I can use the lenses from the 40D (I'll keep the body anyway) but I need to get some longer and faster glass as well. Again, appreciate the reply.
6D does sound like the better choice for that. Just make sure that if you have any Canon brand EF-S mount lenses they never get put onto the 6D. Might break the mirror. Tamron & Sigma don't have anything that protudes back into that area, or if they do I haven't seen one.
Homework first; purchase when done. I happen to like night photography too, & the newer bodies offer a big improvement in usable higher ISO's. You'll also see a noticible difference in the DOF of full frame, it's shallower at wider apertures
I know what you're saying. I am going to be doing more research but I understand how these newer ones do better at high ISO's and longer openings (my son shoots astronomical and sometimes uses a 15 minute exposure (all computer controlled, of course with his telescopes). Noise has been a problem on much of my attempts and I think the 6D will help me overcome that (along with some better lenses).