ATI Radeon HD 3870 X2

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The Radeon HD 3870 X2 manages to outperform every other single card solution in our tests, being bested only by the 8800 GT SLI which is a good $150 more expensive than the ATI solution. It's worth noting that it looks like AMD had finally solved its DirectX 10 performance issues under Bioshock; it's not just that the 3870 X2 performs well, but AMD's driver team seems to have done some good work over the last few driver revisions.

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http://anandtech.com/video/showdoc.aspx?i=3209&p=3