There's no right answer. To be clear, we should discussing:
a) i5-4670K, or
b) i7-4770K
There's no good reason to get the previous gen CPU's.
Last I checked the i7 was about $100 more. If you can find a good deal, get it. In MOST games it doesn't matter. In multi-threaded apps like Handbrake you can theoretically get up to 30% performance out of the i7 but that's a maximum so 20% might be more realistic.
Future games will use the i7 better. Some can already by as much as about 10%.
BUDGET:
That $100 can go somewhere else as well such as a better graphics card. If budget isn't too much of an issue, get the i7. If it factors into buying a better card, monitor, speakers or anything else I'd argue more towards the i5.