what to upgrade next

hello guys,after reading about the overclocking i decided build the rig for gaming i choose go for overclocking and SLI.after i saw all beauty (what that set-up gave me)in the BF3 then BF4 i was too busy gaming and i skip overclocking and SLI part.now i change my minde and i wanna go with higher performance like 4k display and 3d gaming what should i upgrade ,with budget 500$.thanks all for input. my set up is.

  • cpu:i7 3770k

    • mobo z77-ds3h
    psu fatality 750w 80+bronze

    • memory corsair vengeance ddr3 2x4 1600mhz G.SKILL DDR3-1600 PC3-12800 4096MBX2

      • SSD 2.5 OCZ agility 4 256GB

        • HHD 3.5 250gb
          case:Cyberpower APEVIA
        GPU EVGA GeForce GTX660 SC signature 2 GDDR5 2GB PCI EXPRESS 3.0
    cd/dvd LG blue-ray
 
Solution
i would buy a new card, like the 780, or you could crossfire another 660 and get a haswell cpu. but for bf4, I would just get a single 780 or r9 290 :p