I already know that I can use a 3.0 Card on a 1.0 Slot, but does anybody know what the performance drop will be?
I am thinking to buy an HD7750. I have noticed that PCIe 3.0 cards run on less power at load than PCIe 2.0 cards and my power supply is only 400W. But if the performance drop is to big then I will start looking at some PCIe 2.0 cards.
you will see a performance drop of less than 1%. the 7750 isnt all that powerful and even if it is gtx690, you wont see much of a drop anyways. video cards are not even using up all the bandwidth provided by pci-e 2.
therefore your video card can run nicely in a pci-e 1 or 2 system. 400w should be more than enough. the 7750 doesnt need any auxilary power plugs
contrary to what others have said, it is not fully backwards compatible. pcie1 slots provide less power, and some pcie3 cards may work on them while others don't get enough. Sometimes a bios update will fix this so check your motherboards bios update release notes.