Canon 7D with 100-400mm IS lens

For several years I have been using Canon 40D with Canon 100-400mm lens mainly for bird photography with reasonable success. I am considering purchase of Canon 7D but have noted some comments on the internet indicating that using​ 7D autofocus with the 100-400mm lens is not as good as with earlier Canon models(including 40D). Any comments regrading this issue would be appreciated(including opinions regarding autofocus with 7D in general)

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Craig Thayer Chicago, IL