While I can only assume that your 6800's cooler was not stock as that would make to sense to transfer to a new card, I would reccomend you go out and buy some Artic Silver 5. It will be worth the hassle. Using a decent thermal grease alone can lower your temps 2C-4C not to mention longevity. Trust me, you will be glad in the longrun.
From personal experience, I recommend getting and using Ceramique instead of AS5 on your video card. The thermal difference between the two is pretty much negligible. The difference is that while AS5 may not be electrically conductive, is IS capacitative. Ceramique is not, and as such, will never cause the problems a stray blob or dot of AS5 might.
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