CPU: Definitely i5-3570k
MB: No need for pricey boards. I recommend Asrock Z77 Extreme4, however if you want something more 'high-end' go with Gigabyte Z77X UD5 or Asrock Z77 Professional.
MEM: 8GB is enough for gaming. You can add more later.
GPU: Money saved on MB and MEM invest in 7970
PSU: 650W is enough for this system, however adding another later 7970 would require a 750W one.
CASE: Fractal Design R4 seems to be a best choice in this price range.
I would recommend getting SSD for system drive. Samsung 840 Pro 128GB.