|It would help to know which K3 you're asking about.|
Any of the cards (PCIe 2.0, 2.1, or 3.0) will work. Your main concern(s) should be the weak 280W PSU & the primary purpose of the upgrade (general use, home theater, gaming, etc). If it's for gaming, the PSU will most likely have to be upgraded. If that's not an option, make sure to choose a video card that won't overload the PSU.