Let me give you guys some facts. When you compare which CPU is better for gaming, it really depends on what game you are playing.
In general, i5 7xx or i7 8xx will perform better than i7 920/930/950.
Today's most games do not even fully utilize two cores. Same with dual channel vs triple channel memory. Most games only require 2GB. Using triple channel memory setup for playing games that only require 2GB would not make much difference.
Now, even if the game requires more memory for games like Crisis, i5 7xx or i7 8xx can still perform better than i7 920/930/950.
i5 7xx: Advanced turbo technology on single core operation. no hyper-threading.
i7 8xx: Hyper-threading. dual channel memory setup.
i7 920/930/950: Hyper-threading. tripple channel memory setup.
Now depending on games, studies show that the hyper-threading technology that i7 has can reduce the game performances. I do not have direct reference to it but I will leave it up to you on researching that information.
But as I described above, i5 7xx series has advanced turbo technology on single core operations and i7's do not have that.
Because of this, i5 7xx usually performs the best in general games, and i7 8xx or 9xx performs the best when you play games that benefit from hyper-threading technology.
But like everyone agrees, there aren't much differences. But if you are using your system mainly for gaming, I recommend getting i5 750/760. This will last at least 2-3 years for playing mainstream games at close to max settings.
You can rebuild a new system after 2-3 years with the money you saved from going i5 750/760 instead of i7. There is no doubt that i7 9xx is more future-proof, but trust me, Intel will produce more i5 CPU's as well as more i7 even after they bring 6/8 core CPUs in the future. You can upgrade to a newer i5 CPU if you need to feel an upgrade.
FYI, if you are a CPU heavy overclocker, then I would recommend i7 920/930 because they have alot of rooms to increase your performance. But if you aren't heavy overclocker, then i5 750/760 still has good enough room for some moderate overclocking. I am personally against heavy overclocking because of its risks and extra cost on cooling and designing your rig for heavy overclocking.
When it comes down to the cost of building a rig, you can get i7 930 for $199.99 and i5 760 for $159.99 from Micro Center. There isn't much difference to the price but you have to get more expensive motherboard for i7 that uses LGA 1366 socket, and triple channel memory setup also can cost more even though you can still use dual channel operations.