A fourth gen i7 would require a whole new motherboard. Both your processor and graphics are holding you down a bit, so let's take two scenarios.
Scenario 1: If you get a new processor, it will be able to perform more calculations on data so you will be able to play modern games at 60FPS probably on low/medium settings (I'm not sure how good the hd7770 card is). With this current CPU if kept, you will probably not get over 40FPS (which from a personal standpoint does not matter to me).
Scenario 2: If you get a new graphics processor, you should be able to play games on high/ultra for sure but you will just have a reduced frame rate down to 30-40 because of the processor. Take note that a reduced framerate usually means you...