I use the 7DII, 5DIV and 5DS R. There are differences among these cameras.
AF; 5DIV is better than 5DS R, which is better than 7DII. This is both in terms of locking on and reproducibility of focus. I get keepers in that order.
Noise; the 5DS R is best because it needs less sharpening, at the expense of the occasional Moire. I find the 5DIV no better than the 5DS R in general, and both better than the 7DII, despite the comments in that review.
Field of view; the 5DS R wins out by having the reach of a crop and the FOV of FF.
Frame rate; the clear winner is the 7DII. But, like Art Morris, I tend not to fire the camera like a machine gun, but if I need to I will use the 7DII.
Narrower focus; the centre point focus is indeed best on the 7DII.
Quality of glass required; both my 300mm f2.8 II and 400mm DO II virtually max out with the 1.4xTC on the 7DII and 5DS as the hit on going to the 2xTC means that the sensor is beginning to out=resolve the lens. But, both those lenses resolve better with the 2xTC than the 1.4xTC on the 5DIV (and will do so on the 1DXII and 5DIII etc).
If you can't good results doing bird photography with all of these, find a new hobby.