Gottria wrote in post #4896242
Having a 40D and shooting mostly my kids baseball/softball/soccer with the 70-200 2.8. Having good success with the combo I never even thought of jumping to a 1d series body. I have an opportunity to get a used 1dMKII from a friend at a good price, $1400 W/ 2nd battery. I was going to sell the 40D to help fund the 1dMKII purchase but decided to keep it as it's lighter and easier to carry with the family.
I shoot 9-11 year old little league baseball and soccer and my daughters 6 year old softball. Baseball is MUCH easier to shoot than soccer. I know that the 1dMKII will be a better camera for the sports stuff but as an all around camera I think the 40D does just fine.
I don't shoot sports, but I am serious about my wildlife shooting, which includes shooting plenty of moving subjects. I had a 1DII, and I thought it was a fantastic camera, and I can't blame it for ever preventing me from getting any shots that I needed to get. Currently, I'm using my 1DIII as my primary body and a 40D as a second body.
While the AF of the 1DII is truly first rate, I've been amazed about how much better the AF is on the 40D than it was on the 20D/30D. Like with the 1DII, I really can't blame the 40D AF for losing any shots. My judgment would be that the in-focus rate on the 40D (using the center focus point) is very close to what I was getting with the 1DII, and both of those are just a little behind what I get with the 1DIII. Of the shots in this eagle gallery, about 2/3 were taken with the 1DIII, and the other 1/3 were taken with the 40D.
http://www.wildlifeimagesbyles.net/Eagles/Eagles_7/eagles_7.html
The bottom line is that, if I'm doing my job in using the camera properly, I can get the shots with any of the 3 cameras, and, with any of the 3, I'm accustomed to seeing bursts of shots with virtually every shot in focus.
So, I would not consider any AF advantage of the 1DII to be the main reason for choosing it over the 40D. On the other hand, the ability to shoot 8 fps, build quality, weather resistance, etc. are nice advantages for the 1DII, and $1400 seems like a fantastic price, unless the shutter has 300,000 actuations. Just a handful of months ago, you would have had trouble finding a 1DII for less than $2000.
However, don't underestimate the effects of going from a 1.6 crop to a 1.25 crop and in going from 10 mp to 8 mp in terms of what it is going to do to the effective reach of your lenses. Going from the 40D to the 1DII is going to dramatically change your 70-200. The combination of fewer pixels and the smaller crop factor is going to reduce your ability to crop (and still keep the same number of pixels on the subject) by about 40%.
Further, my experience in using both the 40D and 1DII is, contrary to a post above, that the 40D does better at higher ISO than does the 1DII. My 40D files, when properly exposed, at ISO 1600 are about as clean as the 1DII files were at ISO 800 (and both of those are about the same quality as the 1DIII at ISO 3200). There is also no question that the 40D has significantly better dynamic range. I find that the 40D files are much easier to work with. They are more forgiving in terms of not blowing out the highlights, and it is much easier to recover shadow detail with them.
The 1DII is a fantastic camera, but it is a generation older than the 40D, and, because of significant technology improvements between those generations, the decision to go from a 40D to a 1DIII is not as clear cut as many might lead you to believe.