What resolution and graphics settings do you want to run BF4 at?
As is I see no reason for serious upgrade. Your Sandybridge i5 will not be far behind in gaming performance from the latest i5 Haswell and you already have the best GPU on the market. 8Gb should be fine, but if you find that your PC is laggy while playing Battlefield 4 just drop $100 on another 8gb to put you at 16gb (assuming you have 2 free memory slots) and you will be golden. But I wouldn't consider upping your memory until after you try Battlefield 4 because it might not be necessary.
Additionally Battlefield 4 beta with the GTX 770 gets a minimum of 49 fps and an average of 59 on Ultra 1920x1080. This is pretty good and I think performance will only improve with the official release.
^http://www.tomshardware.com/reviews/battlefield-4-graphics-card-performance,3634-8.html