You are planning to buy a EVGA GeForce GTX 680 Classified, correct?
If so this card will be immensely too powerful for a system that is still using pci-e 1.0.
I would say you should upgrade the other parts on your PC before spending so much on this GPU.
What CPU are you running?
What is your PSU and how much power does it output?
What is the exact model of your motherboard?
What resolution is your monitor?