I have both a 7D2 and a 5D3 and for wildlife I almost exclusively use the 7D2. The AF is considerably better for fast moving subjects, and although you can have up for the loss of effective focal length by cropping, the subject needs to be a certain size in the viewfinder to lick focus on, so that only takes you so far for small subjects. For portraits, weddings, parties etc the 5D3 is brilliant, but for birds in flight and fast moving mammals, especially heading towards the camera, I find the 7D2 much better. Plus the 5D3 has a much noisier shutter, so I have use it on silent for close wildlife (I sometimes take both cameras to a hide) which slows down the fps.