Which CPU Should I Get for My New Gaming Rig?

You already have z97 so that limits you to the 4790k or 4690k. I would go with the 4690k unless you plan to do rendering then go with the i7.

The i5 should work fine. The i7 will help but it is not needed necessarily if you are just gaming. It will help some but it mostly is on to your graphics card.

There is already new CPU's out from what your build shows. They released the i7-6700 with DDR4 RAM and a new socket.

60 FPS @ 4K, keep dreaming.
Get the i5

Better get 2 of them if you want high settings.

There are a number of games which have trouble hitting 60fps with sli'd titans much less a 980ti and that's at 1080-1440p let alone 4k. I'd love to hit 120fps at 8k but expectations need to be a bit more realistic. It will greatly depend on the game and most 4k setups are looking at sli. This article shows a comparison of single vs sli 980ti's, single averaging 35-40fps at 4k, sli'd 980ti's averaging 65fps. Some games like gta v won't hit 60fps even with 2 980ti's and witcher 3 shows around 40fps with 2 980ti's. Batman arkham origins will get close to 60fps on a single 980ti.

http://www.maximumpc.com/nvidia-gtx-980-ti-2-way-sli-crushing-performance/

As you said, intel releases new cpu's rather frequently. Does it mean they're outdated? Yes and no. Technically sure, but with each iteration of cpu giving around 5-10% improvement it would be a pointless waste of money to upgrade every time a new chip comes out. In real world performance it will be hardly noticeable aside from lightening the load in your wallet. Anything you get will be 'outdated' in short order so I wouldn't worry about it. Especially considering 5yr old i5 2500k's are still handling current games with ease and they became outdated by sandy bridge, again by haswell, haswell refresh, devil's canyon, broadwell and now skylake and yet it's still a flip of the coin if someone with a 2500k should bother with skylake or not. Outdated doesn't mean worthless by any means.

Black friday is 3mo away yet which is almost an eternity in the tech world especially when it comes to pricing. No telling what will happen. The 6600k may be $5 off its normal price, the 6700k might be slashed $60 on a one day sale. Too many unknowns to make suggestions based on a sale that hasn't happened yet.

The good news though is that regardless of whether you go with the i5 or i7 you'd be hard pressed to get poor performance. Last black fri the newest chip was the 4690k/4790k and they were marked down lower than their predecessors (4670k and 4770k). If they do the same thing this year, the 6600k/6700k's will be getting the price cuts but it's all speculation at this point. Another thing to keep in mind, have an idea of what current pricing is closer to the sales. That way you'll know what's a real deal and what's not.

Keep your credit card handy and really watch the various sales at newegg, tiger direct, ncixus and amazon. Sometimes the sales are flash sales and could happen on black fri, the day after, cyber monday etc. Popular parts sell out quick, think of it like a virtual marketplace stampede similar to the crowds gathered around brick and mortar stores for doorbuster sales. They also like to play with pricing daily and sometimes hourly. The 4690k last year was originally retailing for $239, during the holiday sales it jumped from $208 to $214 to as low as $204 back to $229.

My suggestion on the current build you have listed, you're looking at some nice cpu's and definitely nice gpu's. I would consider something besides bottom of the barrel motherboards and cpu coolers. Especially since all the models you're referring to seem to be k series so I assume you're looking to overclock. The 212 evo was a decent cooler in its day and it's hung in there but there are better designs and more capable coolers out there.

Over time ddr4 could be beneficial if for nothing else because it will be readily available. I'm not sure how long ddr3 will be easily obtainable or at what prices, as ddr2 has been phased out supply isn't as high as it once was and so it carries a premium. This was true before ddr4 became available. I'm not saying 4k will be hard to achieve with a 980ti but we're sort of at an in between period where a 980ti is more than needed for 1080p but not quite enough for 4k on its own (at high frame rates). Maybe split the difference and go for 1440p with a 980ti? It may be a tradeoff of moving to a higher resolution in 4k but having to turn down many of the visuals to get decent frame rates.

With 4k still being relatively new and only adopted by a few enthusiasts at the upper end (not mainstream), the hardware is still in its infancy supporting it at the framerates we've gotten used to with lower resolutions. Especially while using a single gpu. Before 4k really takes off, not only will pricing have to become more attainable for most people (high cost of 4k screens) but hardware itself will have to play catch up in terms of wider gpu support. Being more or less niche right now 4k is going to come at a premium so you may be looking at $1200-1500 in gpu's alone to get smooth 4k game play.