Here's what i'd kinda push for if i had about $800 bucks to spend.
http://pcpartpicker.com/p/cqP3jX
That Athlon is an AMAZING cpu for the money. it's on par with the A10 7850k just without the internal graphics. and with an R9-290. you'll get absurd performance, 3 Free Games, Mantle Support, True-Audio support, and all the goodness of AMD's Catalyst Omega that they just dropped.
IPC seems to just be 10% better than the 760K, but then again there aren't a whole lot of benchmarks on this chip atm. It looks like the die shrink helped, but not a whole lot.
it's 10% better and it performs exactly like a 7850k in the CPU side. and it's $70 i don't understand the issue. extra performance is extra performance. on top of that with CPU cooler i added into that build, he'll be able to pull at least a 4.5 or 4.6ghz overclock on it. if his focus is gaming, he should be focusing on the GPU side of the equation anyways. so the build is fine in my opinion. in the real world, he really won't notice the difference in performance unless he goes looks up performance numbers and compare it to Intel-Based systems. on top of all of that most games now-a-days are GPU bound, thanks to AMD's Mantle, and Microsoft getting on the Ball with DX12.
I know that the 860K performs exactly(or a little bit better actually, since there are less power limitations due to the iGPU being absent) than the 7850k. Also, the 7850K was never THAT strong on the CPU side. As I stated, it seems that the die shrink to 28nm is a major factor for the 10% IPC performance. It's still using a similar design - 2 modules(this time, steamroller) with 4 integer cores.
I suppose for $70-80, it's great.
I have looked at some overclocking results awhile back on this chip, and most results ended up being that 4.6ghz was pushing it for stability. I highly doubt he'll get more than a 1ghz overclock unless it's a golden chip. Maybe the yields have been better for 28nm, but I'm guessing at this point.
It would work well, but you are not spending money wisely.
If you're going with a non-k cpu, then go with a cheaper motherboard with a H97, B85 or H81 chipset. This way you can save $30 - $60. Here are a few good examples : H97, H81.
You can also get some cheaper ram, if there's any available, for further savings.
http://pcpartpicker.com/p/2tckRB - no storage
http://pcpartpicker.com/p/jqK7nQ - $785 with storage
http://pcpartpicker.com/p/xPtCqs - $752 with storage
I like your build, the only thing that bugs me is that your CPU isn't a K processor.(its nice to be able to overclock it) If you are able to squeeze a small SSD in the build for your OS it will make the world of a difference.
I don't see the point of crashing down to a 860k over the i5... save money? sure... but you're sacrificing a LOT of performance
http://pcpartpicker.com/p/B6hjsY
same CPU... cheaper mobo since you can't overclock it... much better GPU, added an SSD... still under the $800 mark... and I would highly recommend an SSD to ANY build... it's the biggest performance increase you can get short of a nice GPU... and if you're not gaming or doing GPU-accelerated tasks, it's hands down the biggest performance increase you can invest in... it's not just boot times like some people lead you to believe, it's loading times period... though now that I have all my games on SSD storage, I wouldn't recommend wasting money on game storage...