i will be pretty upset if the 7xxx comes out only marginally better for mining. Because i just sold both 5970 at $300 a pop on ebay getting ready for the 7xxx series. Miner is down right now waiting for the new card to release.
well my reasoning was the new gfx card will be released in the next week or two, causing the older models to drop in price significantly as this is a full refresh not just an upgrade. So if 7xxx isnt all that hyped up to be for bitcoins, i should be able to score some of the older cards at much lower price otherwise i will just get a pair of 7xxx. The one thing i didnt want to do was holding onto an aging pair of 5970 that will be two generations old.
If it was some cheaper $150 card i would probably just kept it, but at $300 a pop they can still lose quite a bit of value quickly.