Just buy the 260x and a new power supply and start slowing going towards a whole new system. You will be bottle necking the card by about 40-50% in games like that. If you play something like am mmorpg then it wouldn't cripple the performance all that much. If you do chose to go by what I just said go power supply, video card, case, motherboard,ram,and processor. the last 3 should be bought together. You can also add an sdd and hard drive once you have extra money. all of those games use 3+ cores not 100% about cod but I would guess 2.
But I don't have the budget to upgrade my whole rig. So just if you can recommend best gpu that won't bottleneck and run mentioned games at low-med or high settings at 30+ FPS.