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 by
sleepnever, 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.