Pretty much all the 6800GT cards use the same heatsinks, making them all about equal. BFG, GainWard, and LeadTek use different heatsinks. BFGs, is just slightly better than stock, Gainwards is just slightly better than BFGs, and then the LeadTek is the best.
LeadTek is known for having massive heatsinks, and consquently are known for haveing good overclocking abilities. Personally I have own two LeadTek cards and have been impressed by both.
Check out the pictures of the LeadTek card: (You'll see what I mean
)
<A HREF="http://www.newegg.com/app/ViewProductDesc.asp?description=14-122-195&depa=0" target="_new">http://www.newegg.com/app/ViewProductDesc.asp?description=14-122-195&depa=0</A>
To overclock it all you need to do is download RivaTuner. RivaTuner will allow you to adjust GPU and RAM speeds. There are other programs that will allow you to do this as well, RivaTuner is what the majority of people use.
My Desktop: <A HREF="http://Mr5oh.tripod.com/pc.html" target="_new">http://Mr5oh.tripod.com/pc.html</A>