http://pcpartpicker.com/p/1QdUR changed the gpu and some other stuff
I know you want to build a computer to rival the physical build of a modern iMac but it's entirely not necessary.
A far cheaper computer could render a high definition photo just as good and better (depending on the users skill) than a top dollar iMac.
To put it simply, my 800 dollar computer can render a photo better than or equal to a 3000 dollar iMac computer.
I know it's your decision in the end, but I hate to see someone throw so much money away because they think they need a sports car just to drive down to the convenience store every sunday.
I mean, looking at your build, you've got a liquid cooling unit for your CPU, your processor will never get hot enough for this to serve it's purpose, you're only editing photos. 32 gb of ram for multitasking? Even hardcore gamers can't multitask enough to utilize that much RAM. Why do we keep using gaming as a reference? Because it is one of the most intensive things that commercial computers have to handle, the graphics card has to render polygons, vertices, lighting, 3d effects, 2d effects, physics, etc. All a graphics card has to do for Photoshop is render and map pixels onto a 2d plain, maybe add a lighting effect here and there and that is ALL. The graphics card you want to purchase will be sitting inside of this computer moaning to itself, "Why the heck am I here?"
It's honestly just kind of frustrating that you come into a tech support forum, ask for help, then disregard all of the advice given to you, heck, TBC1 even went out of his way to build you a custom build that would serve your purposes greatly and save you over a thousand bucks.
Please, I beg of you, take my word on this, I graduated college with a digital filmmaking degree, a medium that is more computationally intensive than photography. I worked alongside photographers. If your computer is more than a filmmaker would need, then it is WAY more than a photographer would need. We only want to help you, if you're honestly just building a computer for photography then save your money or donate it to a charity and save some childrens lives. If you're just pulling our legs, then just buy the thing with the works and all the bells and whistles.
I just can't let this one go without giving this advice. THINK OF THE CHILDREN.