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You referred to a card that is not offered in the retail market, and should not be referenced in any official materials. That is what is called an "OEM only" product. The HD 5750 is currently the accurately named device that was sold widely while it was in production (although that was several years ago now, and the R# 3xx series is the current generation). Working backward, that HD 5nnn generation was four generations ago, and would be hard to find at retail today.
FYI, there was never any individual GPU with the name "HD 6800". There was an HD 6850, and an HD 6870. I don't think there were any others. Your crashing is most likely caused by failing to update the the very latest drivers that ATI / AMD offers (those from Microsoft do not count as "current", since their driver library is always very far behind).
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