I was already expecting the Sapphire X800 GTO Ultimate to overclock well but my expectations were blown away. This card reached 617 MHz on the core and 1146 MHz on the memory. The memory clock is good, but the core clock is mind blowing. It?s a 54% overclock! I?m not sure if I?ve just been lucky or if this is indicative of what you can expect on these cards, so I tested another X800 GTO I had to hand.