"the sensor of a crop camera is over loaded by this lens and therefor the images are not as sharp as they would be as on a full frame body"
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Huh?
The 70-200 works quite well on a 40D. In fact, every Canon telephoto that I have tried works very well on a 40D. Images are crisp, focus is quick, and the 1.6x lens factor gives me a little more reach that sometimes comes in handy.
The only downside to using the 70-200/2.8 is balance -- even with the battery grip, the 40D is much lighter than the 1-D series cameras, and the combination balances differently. For this reason, I like to put my 40D on my 300/2.8 and put the whole thing on a monopod. Great combo.