The Sapphire one has a clock speed of 580MHZ, and an effective memory speed of 1400MHZ. The Powercolor one has a core clock speed of 575MHZ and an effective memory speed of 1380MHZ. The Sapphire one has 512MB of DDR3 RAM, while the Powercolor has 256MB DDR3 RAM. I believe that the Sapphire one is the better performer.
The Sapphire card retails for about $220, while the Powercolor costs $240 (with rebate, however, the price is $195). The Powercolor model also has a larger cooler that takes up 2 slots, so be sure it will fit in your PC. While the Sapphire one performs better, the Powercolor card is cheaper with a rebate. If you are not going to be gaming on high resolutions, the extra 256MB of DDR3 RAM will not make a very large difference. The difference in their clock speeds (core and memory) are negligable.
So, if you game on lower resolutions and have the space to fit the card, I'd recommend the Powercolor model. If not, I would recommend getting the Sapphire card.
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