Actually, even though the 6800XT has 8 pipes instead of 12 like a real 6800 (vanilla), the highest clocked 6800XT's can beat a 6800. But those are rare. I'd say the 350 mHz core 1000 MHz mem ones are pretty good, equal to above a 6600GT. But the 350/700 or slower ones are slower than a 6600GT.
Anyway, when talking 6800XT, saying avoid them is a safe bet. But in honesty it takes knowing the specific clock speeds to see if it could be worth buying or not. Anyway, reguardless of it's clock speeds a X800GTO would beat it out and maybe cost you the same or less.
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