We would have liked to deliver further results for the GTX 260 but the Nvidia sample was not fully functional when it reached our office. Only very few tests could be made with the card, which reached critical temperature within seconds most of the time and shut down. The card itself didn't heat up actually. Even a remounting of the cooler didn't solve the problem. Therefore think the problem is caused by a defective temperature sensor or because the Die doesn't have contact to the heatspreader.
Sloppy work from the looks of it...