GTX980 and 4690K would be better for gaming because of the superior graphics card.
Virtually all 4690K can do 4.0 with a modest air cooler.
Because the 4790K is better binned, it can probably oc to higher limits.
But... do you really need any more than 4.0?
Any OC will up the voltage some.
So long as the voltage does not go over 1.30, you will have no issue with longevity or heat.
I have become a bit jaded on the subject of haswell cooling for overclocking.
How high you can OC is firstly determined by your luck in the bin lottery.
I had high expectations from the Devil's canyon parts and their better thermals.
I found out that the thermals really do not matter unless, perhaps, you are a competitive overclocker.
Haswell runs quite...