It's not so simple to answer that question. What are the clock speeds of the 6800XT? They vary so much with 325MHz, 350MHz, and even 425MHz core speeds and memory from 600, 700, 900 and 1000 DDR. If it's a 350/1000 card, I'd put it ahead of the X1600 pro the majority of the time. If it's one with the slower 600-700 memory, then I'd put the X1600 pro ahead. If it's clocked 425/1000 like the Galaxy 6800XT, then it easily is the winner.