If you have $1600 to throw around, here is what you want in a Gaming PC:
Intel CPU - Core i5 with Quad Cores. Preferably the 4690 or 4690K if you plan to do overclocking…
Core i7 are more expensive because they have hyper threading, but hyper-threading does not improve gaming performance most of the time.
8GB of RAM. No less then this. More then this is optional, but not really useful unless you plan to run virtual machines. RAM speeds vary, but generally do not affect the game much. 1600 is usually the middle ground between the speeds for DDR3 RAM. 2133 is considered more gaming grade speed, but again, probably would not even notice the difference.
If you get an SSD, it will improve bootup times drastically, like 15 secs to desktop. But will not really improve gaming, just improve load times. So only install things like web browsers and Microsoft Office or Photoshop. Minimum size should be 120-128GB. Preferably 256GB so you have lots of breathing room and can install a game or two to reduce loading times. Anything smaller and you will run out of room quickly.
Hard Drive should be 1TB minimum. 2TB preferable. This is where you will be installing the bulk of your games, random programs, and store your media/photos/music. You might get away with 512GB Hard drive, but you will run out of room fast.
If you are not going to mess around with overclocking, the motherboard you get does not really matter. If you are going to mess around with it get a motherboard with either H87, Z87, H97, or Z97 chipsets. Basically its fancier chips on the board that let you do more with the settings.
PSU for gaming minimum should be something like 500Watts, but it really depends on your load that your other components will draw. But as a rule of thumb, its better to have more then less. So 600-750Watts if you plan to run multiple graphics cards. As long as it is a quality name with good reviews, like Corsair, Antec, EVGA, etc, you should be fine.
Refer to this chart for how strong a card is compared to others:
Get a graphics card with at least 2GB of VRAM, but 3GB or 4GB is more preferable for future proofing.
Something like a GTX 970 from NVIDIA or R9 290 if you prefer AMD.
SLI vs Single graphics cards:
I’m of the school of thought that I prefer a single powerful graphics cards, since not all games support SLI/Crossfire. But games that do support SLI get a nice graphical boost out of it.
And most importantly, I cannot recommend this enough, if you are going to spend that much money on a gaming PC, please buy a UPS (Uninterruptable Power Supply) Basically its a battery combined with a surge protector. It keeps your PC running and protected from power fluctuations, lightning strikes, etc.
Something like this: http://www.newegg.com/Product/Product.aspx?Item=N82E16842101430&cm_re=500_watts_ups--42-101-430--Product
Make sure you check the amount of Watts it can handle, not the VA. VA is not the same as watts. You probably want something in the 500-750Watt range. The bigger the watts it can handle, the longer it will last if the power goes out.