I upgraded from a 40D to a 7D and love both cameras. I thought going from a 10meg to a 18meg pixel camera it would make a big difference with cropping. I am not able to explain it (I imagine someone will jump in and add detail) but you do not get the additional cropping you would think even though there is a large jump in pixels. Focusing on your wish list, getting a 70-200mm zoom might be the best depending on what you are shooting.
Even though I will probably get slammed for saying this, one word of warning. The 7D required a much longer learning curve than I ever expected jumping from the 40D. It has taken me months to get the hang of it to get some of the same quality pictures I achieved easily with the 40D. I will say this, once you get the hang of it...the pictures are outstanding and you will not want to use anything else.
I included a 7D picture taken at ISO 3200 to help you see what you get. (Taken raw and processed in CS4 with no noice reduction software.) I typically do not like using a high ISO, I never went above 1600 with the 40D and still struggle with it on the 7D. Even with the 7D the quality is never the same but I like having the option knowing I can still get a good/usable picture without a flash beyond what I got with the 40D depending on the situation/lighting. Sorry, I hope I am not making this choice harder for you. I struggled with the choice to spend another $1600+ on my favorite money pit of a hobby, so I understand your dilemma. Good luck with your choice!
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