The calculation below is correct, except for one thing:
These are the speed of GPU (graphic performance, as claimed by Apple), not CPU.
So what this means is that the GPU of Air and Mini retina should be similar and only difference may be frequency. This is understandable as both Mini and Air have same resolutions
However, the CPU clock may be different
because apple's claim is infact
iPad Air is 2x faster in both CPU and GPU than the iPad 4 A6X
The A7 in the iPad Mini Retina is 4x faster in CPU and 8x faster in GPU than Ipad mini A5
So see the difference? CPU is 4x, not 8x. So looks like the CPU in mini retina will not be same as air, only about half of the performance if I estimate correctly.
Welcome to correct me if I am wrong