You can most likely run it, but you will take a small performance hit. Not sure how much though. A few sites in the past has done tests using high end cards on PCI-E 1.0 slots with high end 2.0 cards they found something like 5% performance hit or around there when they used it in a 1.0 x4 slot. And that x4 slot should be equavalent to half the speed of a full x16 pci-e slot for max bandwidth. So even taking differences into account I suspect it will still work for a good performance increase but it won't be as good as if you had a full x16 slot as I still suspect something along the lines of 5-10% performance hit.