Either option is going to be held back by that old CPU. Unfortunately you have pretty close to the best CPU that motherboard supports, so any meaningful CPU upgrade will require a new motherboard, and probably new RAM too. Your options are to buy one of those cards now, and accept that they won't be performing to their full potential until you do a rebuild on the rest of the system, or step down to a lower end card like the HD 7770 or GTX 650Ti, which won't be held back by that old CPU.
