I agree with others that the shot of the lion with the child is fantastic! Great shot.
With regards to the camera, I don't know if one trip to the zoo would help you decide. It really comes down to what you want out of your camera. I moved from a T2i to the 5D3 because I wanted FF for wide angle, low light performance, better AF perf, weather sealing, etc. I love it and while I have come nowhere close to mastering the AF, it hasn't done me horribly wrong yet.
Here's a shot I took last saturday at our zoo with my 5D3 + 100-400. I was using the center point + surrounding in AI Focus through 3" of curved glass while this guy was on the move and the AF nailed it. 2013 Jaguar WPZ
, on Flickr
I'll also be shooting a newborn and after that a roaming toddler around the house, so this will be great. The lack of AF system on my T2i and the 6D is why I went with the 5D3 in that area.