Idle is 56 degrees it says, and to me this doesn't seem bad...
but 80 degrees, especially using a fan you've added should cool it more than that, with the standard ones usually cooling cards to around 70 degrees, and so a more effective one should be getting this down to 60's, maybe 50 degrees in heat when in full use.
I would advise checking that the fan is secured properly to the card, maybe checking for the stuff you put on it beforehand and maybe placing more? So just check this, since that should be cooling it more than it is, so something seems wrong there.
If all seems to be working correctly, since the 6800GT is a powerful card, it might be normal and so I wouldn't worry. Video cards tend to get very hot, and a temperature reading of 70 degrees is not unknown, even on weaker cards, and they can handle heat better than processors can, because a processor at that heat would be advised to be turned off as it could be causing it to slow down and even risk crashing the computer.
I hope this helps