Ha, we all would!
Having more cores will help ensure that a game runs more smoothly, even if the average FPS is the same on an 8 vs 4 core cpu. Here's a video on that.
[video="https://www.youtube.com/watch?v=-GgDZKGA89I"]https://www.youtube.com/watch?v=-GgDZKGA89I[/video]
But the only way to tell is either find reviews of core utilization online or else test the games yourself.
For some games that are very poorly threaded, which overload one few cores without even addressing idle cores, the 4 core 4970k would actually outperform the 8 core 5960x. Each core in the 5960x is a little slower even after overclocking, so a game like that would run slightly slower. The good news is that most games aren't that bad, and even the bad ones only suffer from it during limited contexts during gameplay (i.e. really intense scenes).
I know that Boarderlands 1, 2, and the Pre-Sequal are very poorly threaded, whereas games on the CryEngine (e.g. Crysis 3, Evolve, etc.) and both Far Cry 3 and 4 spread work pretty evenly across many cores.
Also, when people say all you "need" is a quad core i5 for gaming, they aren't technically wrong, but it's a qualified statement. You'll be able to run most things on an i5, but you'll have to close other programs in the background, and it still might not be as smooth as an i7 in demanding titles. As for going higher than that, it's really a luxery that helps in a small percentage of demanding games at high settings. X79 and X99 are really for workstations and high-end gaming configurations. That said, I'd recommend getting the best chip and platform you can afford.