I am looking to build a gaming computer, with a focus on the most power for the least amount of money. So far, I really like the i5-3570K, but am struggling how to pair it up with a GPU.

• Since the K model is capable of doing so, should I overclock this CPU? Will it improve the performance noticeably and how difficult is it to do so? Overall, is it a safe procedure, so long as I am sensible with regards to cooling?
  
• Which GPU should I use with this CPU? I am looking at a pre-overclocked GTX 660 2 GB VRAM or a HD Radeon 7870 2 GB, which I could then always go on to overclock if necessary. Which is better?
  
• With regards to your recommended choices, what sort of performance could I expect from this? Using Crysis 3 as a benchmark, which is one of the most intensive games I can think of from this generation, what sort of FPS can I expect on what graphical settings and resolution? It would be running on 20" Full HD Samsung monitor.