i5-4690k is good spot for gaming right now, and I think it will perform amazing in games for at least another year.
Anyway, as games use more and more processing power with almost every AAA release, i7-4790k would be more future proof.
If you feel that you are not going to upgrade your CPU in 1-2 years, I recommend you to get i7-4790k. Anyway it depends on your budget.