4690k is just fine for gaming. 4790k of course is the "bigger better and faster car of your dreams". For gaming, a lot of people choose the 4690k for the price and because you can OC it, it can get great clocks. The 4790k is a little more high end for CPU intensive users, such as editing, designing and overall multitasking till you're blue in the face.
That said, look at the prices, and check for deals. When I was looking, a few months back, the 4690k was about $240ish BUT Microcenter had an in store deal on the 4790k for about $275ish? After tax the i7 was still $300, but it was close enough that I was able to justify the purchase. I do more than just gaming so I'll get some use out of the extra cores/threads that come with the i7 compared to the i5, but honestly for gaming either will do you well.