How does my gaming rig look?

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You might consider spending a little less on that RAM and a little more on the PSU. I'd be looking for gold or better. General rule of thumb is - the better the standard, the better quality the PSU is overall.
There are exceptions, but this is generally the case.
I think this would be a slightly better option.
https://www.amazon.com/CORSAIR-TX650M-Modular-Power-Supply/dp/B01N18J52E
Unless you're going to power large, low impedance speakers directly off your motherboard, you won't need 750W. I overclock a 980Ti, 4SSD RAID, 32G of ram, 2 HDDs, ethernet, and a whole bunch of accessories off a 550W PSU with plenty of headroom to spare.

Also, you're getting a killer CPU and putting it in an average MB. Consider sacrificing 2 cores for a...
PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 5 2600X 3.6GHz 6-Core Processor ($209.99 @ Amazon)
Motherboard: ASRock - X370 KILLER SLI/ac ATX AM4 Motherboard ($89.99 @ Newegg)
Memory: GeIL - SUPER LUCE RGB SYNC 16GB (2 x 8GB) DDR4-3000 Memory ($170.98 @ Newegg)
Storage: Crucial - MX500 250GB M.2-2280 Solid State Drive ($72.27 @ Amazon)
Video Card: Asus - Radeon RX 580 4GB Dual Video Card ($269.99 @ B&H)
Case: NZXT - S340 (White) ATX Mid Tower Case ($49.99 @ Newegg)
Power Supply: SeaSonic - 520W 80+ Bronze Certified Fully-Modular ATX Power Supply ($34.90 @ Newegg)
Total: $898.11
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-05-25 04:00 EDT-0400
 
You might consider spending a little less on that RAM and a little more on the PSU. I'd be looking for gold or better. General rule of thumb is - the better the standard, the better quality the PSU is overall.
There are exceptions, but this is generally the case.
I think this would be a slightly better option.
https://www.amazon.com/CORSAIR-TX650M-Modular-Power-Supply/dp/B01N18J52E
Unless you're going to power large, low impedance speakers directly off your motherboard, you won't need 750W. I overclock a 980Ti, 4SSD RAID, 32G of ram, 2 HDDs, ethernet, and a whole bunch of accessories off a 550W PSU with plenty of headroom to spare.

Also, you're getting a killer CPU and putting it in an average MB. Consider sacrificing 2 cores for a much better motherboard, or just spending a bit more for a better MB. I like the CPU, but not putting it in that MB.

Memory speed is not as important for gaming as some make it out to be. Blazing memory speed is not going to compensate for a lackluster motherboard, or slower CPU. For gaming, I think your GPU pick is excellent for your budget.

And now for the hard part. If you wait till September, new CPU lines and chipsets will be coming out and that should reduce the cost of older stuff. Problem is, this is the case.... always. If you wait forever, things will always get cheaper.
 
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