Ok but now watch this. By Feb 2011, you could get 6950 unlocked for only $230 + $250 savings from not buying 580 provided 85% of the performance of the 580 for ~2 years before 7970 launched. Sell 6950 for $175 + $250 savings from not buying the 580 = $549 - $375 resale + savings ~ $125 to upgrade to 7970.
Once 7970 was overclocked it gave 50%+ more performance over 580 oc. Therefore, for the majority of competition between 6950 @ 6970 vs. 580, 6970 provided about 85% of the performance and then when it came to newer games, the amount of $ saved from not getting 580 + reinvesting it into a future 28nm GPU blew 580 away.
Therefore, the point for 480/580's longevity is not really that important imo since upgrading more often is the more preferred route. The same thing will happen with 7970GE vs. 780/R9 280. By the time next gen PC games come out, all 3 of these cards will be too slow but right now 7970GE has little trouble with most games since they are still
PS360 console ports. The difference now is even more in favour of the 1Ghz 7970 since they are dropping to $280 which represents a $370-400 savings over a 780! You know how much $370-400 savings + 7970's resale value will get you in GPU power in the next 2 years? I bet 40-50% faster than 780 by the time next gen PC games hit and we
really need the extra GPU power.