I found it a bit disappointing because the gtx 780 would have 2560 cuda cores while the 8970 has the same. Pretty much the same specs such as 3GB & 384bit memory controller. But a cuda core's frequency is always higher. A single cuda core is always faster for gaming than a stream processor from AMD but AMD is winning in GPGPU computing like 5x such as bitcoin mining.
If I'm correct the stream cpu's frequency in an amd is actually the same as the core clock. So for a 6970 they all would run at 880MHz but for example with a gtx 680 the cuda cores are running at 2600MHz.