And yet... you didn't answer my questions. Quite frankly, it is because you can't.
The problem with Fermi relative to GCN is not texturing efficiency or ROPs efficiency, it is compute unit (shader) efficiency, but I digress...
single precision math of a tahiti core is 3.7 terraflops and dual precision is just about 1 terraflop even, while Fermi does 1.56 terraflops single precision
So Tahiti has more than 2.3x the Flops and more than 2.3x the texture fill but only performs ~1.4x better than Fermi. That sounds pretty inefficient to me. /sarcasm