TwekaTown posted a comparison between the ATI Radeon X1800GTO vs. X1900GT from HIS and GeCube

The model sent into us for review by HIS is their “Turbo” edition which means you can overclock the card if you need some extra FPS. While not as impressive as other cards we have received from HIS in the past, you are able to boost the clock speed by 20MHz to 520MHz although the memory clock speeds stays the same, 500MHz (or 1GHz DDR). It does seem like the Radeon X1800GTO is already pretty maxed out as far as clock speeds go so don’t expect too much when it comes to overclocking.

ATI Radeon X1800GTO vs. X1900GT from HIS and GeCube