Geforce 8800 Ultra OC vs GTX 280?

Which one performs better? The Geforce 8800 Ultra OC or the GTX 280? I can get either one of them for $200 but i do not know which one is: more reliable, performs better, or works better in SLI configuration. So if someone could help me find an answer that would be great! I could also overclock the GTX 280 with the EVGA precision overclocking tool.

Specs:
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Processor- AMD Phenom II X4 965 Black Edition @ 3.8 - 4.0GHz ( This came short of i7 920 every benchmark i looked at... the i7 was in first everytime)
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Motherboard- ASUS M4A89GTD PRO/USB 3.0 890GX
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RAM- OCZ Platinum ( 2 x 1gb) DDR3 1333
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DVD Drive- Sony Optiarc 24X DVD/CD Rewriteable drive
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PSU- Raidmax Hybrid 730w Modular Power Supply
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Case- NZXT Beta Evo Mid tower ATX case
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CPU Cooler- Coolermaster Hyper 212+
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Hard Drive- Seagate Barracuda 750GB 7200rpm drive
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Video Card- GeForce Ultra 8800 OC or GTX 280 OC ( might sli the better card )