Some crazy Finnish dudes got some good ol' liquid nitrogen and OCed their card's core to 1GHz. I only got my X800XT to 570. And the X1800XT stock is only rated at 625MHz. So well.. performance-wise, here's your out of this world alternative on how to achieve an ATi version of the 'X1800 SLi'.. buahahah.
http://www.theinquirer.net/?article=27252
http://www.theinquirer.net/?article=27252