Go for 640mg GPU, high resolution, and better performence, or you could go with the GTX version, up to you.
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My rig;
Motherboard: EVGA nForce 680i SLi WaterCooled
Proccessor: Intel Core 2 Quad Extreme Edition QX6800
Memory: Corsair 4GB DDR2 Dominator (4 x 1GB)
GPU: 2x EVGA GeForce 8800 Ultra WaterCooled Sli
Hard Drive: 2x Seagate Barracuda 750GB + LaCie 2TB Raid Array External HDD
Optical: LiteOn 2x Blu ray Sata DVD Writer
Sound Card: Creative Sound Blaster X-Fi Elite Pro 7.1
Cooling: Swiftech Apex Ultra+ Watercooling
Case: Thermaltake Tai-Chi SuperMidi Tower
PSU: Enermax Galaxy 1000W