Buying an i5 today off todays performance suite is insane. One should pay attention not only to what is happening today, but what will happen in the future.
I have already posted results for Skylake.
Here is a comparison for Devil's Canyon:
http://www.anandtech.com/show/8227/devils-canyon-review-intel-core-i7-4790k-and-i5-4690k/5
Haswell:
http://www.anandtech.com/show/7189/choosing-a-gaming-cpu-september-2013/10
Ivy Bridge:
http://www.xbitlabs.com/articles/cpu/display/core-i7-3770k-i5-3570k_6.html
Sandy Bridge:
http://www.anandtech.com/show/4083/...core-i7-2600k-i5-2500k-core-i3-2100-tested/20
The biggest gap between the i5 and i7 is for Sandy Bridge. The trend appears to be going the opposite way of how you suggest. Also, if you're paying attention to DirectX 12, the future is in moving overhead away from the cpu not towards it.
This is the same line of thinking GTX 770 2GB purchasers had when they purchased that overpriced piece of crap. They looked at benches, said it's the best out and ignored the fact that consoles were being released soon and VRAM requirements would jump drastically.
The GTX 770 is not really analogous to an i5. The GTX 680 was re-branded as the GTX 770 in May of 2013, and Intel launched the Haswell i5 4670K in June 2013. While the GTX 770 is pretty lacking at this point, the 4670K is still a great gaming cpu. I know this firsthand because in June 2013 I bought both a GTX 770 and 4670K. I no longer own the 770, but I played a few hours of The Witcher 3 on my 4670K just yesterday.
Getting an i5 now because of BENCH tests, and ignoring how actual users use PCs (generally, I don't close every single process to play a game and I have things in the background running/sites/music(pandora)/etc.) that can all eat your CPU cycles but with an i7 processor? I don't worry about it. Ever. Gimping yourself with 4 threads in a high end setup is just not worth it. Especially if you're getting a high end GPU as there are MANY Games that benefit in the 10+ fps range and bring minimums above 60 FPS from the i7.
If your background workload is so intense that it hits your gaming performance that hard, it probably makes more sense to step up to a 6-core 5820K from an i5 4670K/6600K, than it does to go with an i7 4970K/6700K.
All you gain from the 4790K/6700K is a bit more cache and hyper threading, which isn't going to net you 10+ fps with an intensive background workload. I'm not even sure if a 6-core cpu would do that, but it's certainly more likely under the right circumstances.
edit: don't get me wrong, the i7 is a better cpu than the i5. No argument from me there, but I still consider the i5 a better value for gaming. I put my money where my mouth is too... My gaming PC has an i5, but I made sure to get an i7 in my Macbook Pro, which is used predominantly for music production.