Nice build just a few observations:
There's no extra CPU cooler, so I'm guessing you'll add one and overclock maybe a year or two down the line to extend the system life (which is what I'm planning with my i5 4690K). If you don't ever intend to overclock you can trim the budget with a non 'K' CPU (Toms suggests the i5 4460)
http://www.tomshardware.co.uk/gaming-cpu-review-overclock,review-32901-4.html and a 'H' series motherboard.
If you opt for a R9 290 and intend to overclock I'd add 50 to 100Watts to the powersupply otherwise at stock speeds the CX600 is fine, although plenty here will tell you it uses lower quality parts than some-true-it's only possible issue is a shorter lifespan than you'll get with a full, top notch part but TBH by the time a typical user has reached anything like that level of use they'll be old and grey.
GTX960: Fine for most games at 1080 rez on a single display but it's limited 2Gb of memory is going to be an issue sooner rather than later if you're looking for very high eye candy so look out for the 4Gb versions when you come to 'add to basket'.
GTX970: The best high end part available for the money. Ever. Most expensive option but the performance is just enormous; far too much for most games at 1080 rez unless you get really, really heavy with either DSR or AA. Expect it to last so try for one with a long warranty! If mine hadn't have been such a bi*** I'd still have it.
R9 290: Falls between the Nvidia parts, a good deal faster than the GTX960 and with a standard 4Gb of memory but a little slower than the GTX970.
Burns more power but isn't so fussy about the choice of power supply as Maxwell cards seem to be and produces more heat. Right now it's the best value for raw performance thanks to the current price cuts. The three fan models are the ones to go for if you want quiet. The Carbide case has more than enough ventilation BTW.
For many Nvidia really shines with its added software features like DSR, PhysX, Shadowplay and an extended range of AA options.
AMD has a similar feature to the Geforce Experience/shadowplay with Raptr but has no answer to either DSR or PhysX and #Mantle uptake seems very limited at this time.
I'm just going to say in all the years I've been using PC systems the only driver issues I've had from either company have been self inflicted, mainly caused by non certified third party addons.
DX12 is still, for me at least, a moot point, it'll be at least a couple of years before we start seeing purpose coded DX12 titles in any numbers and until the final code is released and tests are run there's only speculation as to how each card is going to deal with it, I've seen far to many broken promises in the past to do anything more than take a 'wait and see' position.
I think you have all the facts now so it's your choice, Neo: Do you take the Red pill, or the Green?