Google GTX 480 1200MHz - theres atleast half a dozen people who've hit those kinda speeds some of them with 2-4 card setups. I'm yet to find any one whos got a 69xx clock even benchmark stable at +70% let alone every day stable like some of these guys have managed - which tends to be a good sign for overclocking on these cards in more every day settings too.
While the sucess rate for 6950 unlocking is high (about 90% from other figures) and around 70-80% from my own experience I know of atleast 3 cards that have failed - 2 of which belong to people who post on these forums.
Rroff..... half a dozen, If the majority can't run 900Mhz then what use is that?. Lets stick to the stock cooler as that is what I'm using. Not really a good comparison as I've said to you maybe three times now.
I've seen people's cards failing due to not looking after their card appropriately. I've not seen people's cards fail that have tested and understood the limitations for the card though. People who run the 6970 BIOS are risking damaging their memory.
So no GTX 480s have failed?. That is impressive

http://www.google.co.uk/search?hl=en&source=hp&biw=1600&bih=1008&q=gtx+480+died&aq=f&aqi=&aql=&oq=
Not sure what cards you have seen fail, but I have not seen a single card fail to unlock and run at 70 speeds that was unlocked properly, shy of one or two on the memory speeds.
Unless it was some of those that put 70 BIOS' on them and killed them. Which they derserved, but not a fault of the card.
Yes, it seems the people who don't even own the card are the armchair experts in this thread. It's pretty ridiculous tbh.