I was a little disappointed as well since I just sold my 6950's but after reading a few reviews I think the performance difference will be worth it. According to
ComputerBase, the 7970 is 61% faster than the 6950 at 1600p. From early indications the 7970 overclocks like stink and performance scales well. The 6950 generally gets a 8-10% overclock on stock volts and performance doesn't scale as linearly. I know my 6950's would hit 900MHz on the core with 1.175V. On stock volts they were closer to 860-870MHz.
With a healthy overclock the 7970 should be just as fast as Xfired 6950's which is perfect IMO. You get the performance without the power draw and multi-card compromises. Bang for your buck still isn't as good as the 6950's since they can be had for ~$200 on the used market or $230 new, but that's always been the case with single vs multi-gpus.
The only reason I would be disappointed buying a 7970 is if AMD decides to release Tahiti 1.1 in a month or two like they did with the X1900XT.