Hello this is GPGPU, not gaming. You have a common algorithm, not some binary blob that vendors create application profiles for by introducing all kind of tricks to improve performance. No miracles and no marketing gibberish, just simple maths. You have 1536 shaders clocked at 1008 versus 2048 shaders clocked at 925. With GCN, both architectures are now scalar and comparisons are even easier because bitcoin employs  a simple algorithm that is extremely ALU-bound and not memory-intensive and does not involve lots of branching. In the best case where NVidia implemented bitwise rotations and bitselect, difference performance-wise would be ~22% in favor of 7970. And this would also likely require a rewrite of the NVidia miners. As far as mining is concerned and as far as the TDP and prices announced until now are correct, there is no way 680 becomes a better alternative to 7970. Not even close.