Assistance requested - New build

Whats your budget total for the build. I'm assuming you're using existing monitor/keyboard, do you need an OS?

The big downside to the i5 is you're going to miss out on multi threading when you do anything with your editing work.

Here's some suggestions to add to but not alter your build. Its stuff you seem to have left out (assuming they arent coming in from the old build). The PSU is a bit overkill but its a great deal. Otherwise a 500w XFX or Evga B2, G2 or P2 would be great ideas. The X300 is a good drive but a bit slower than something like Samsung 850 evo. However that price is very good. Either one would work well and would likely be a big improvement from what you're on now.
PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor ($244.99 @ Amazon)
CPU Cooler: NZXT Kraken X31 69.5 CFM Liquid CPU Cooler ($73.99 @ Amazon)
Motherboard: MSI Z170A GAMING PRO CARBON ATX LGA1151 Motherboard ($169.99 @ Amazon)
Memory: G.Skill Ripjaws V Series 16GB (2 x 8GB) DDR4-3000 Memory ($84.89 @ OutletPC)
Storage: Sandisk X300S 512GB 2.5" Solid State Drive ($133.99)
Video Card: EVGA GeForce GTX 970 4GB Video Card ($329.99 @ B&H)
Case: Phanteks Enthoo Pro M ATX Mid Tower Case ($64.99 @ Newegg)
Power Supply: EVGA SuperNOVA P2 650W 80+ Platinum Certified Fully-Modular ATX Power Supply ($66.99 @ NCIX US)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($18.39 @ OutletPC)
Operating System: Microsoft Windows 10 Home OEM (64-bit) ($87.95 @ OutletPC)
Total: $1276.16
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-03-08 23:16 EST-0500

Suggestions I'd make.
Ditch the water cooling. With a cheaper big air cooler you can get the same overclock of a single fan closed loop water cooling system. I like the Cryorig line up, the H5 universal would give you hefty cooling but not interfere with any RAM slots.
http://www.newegg.com/Product/Product.aspx?Item=9SIA4UF1W87430

Now if you wanted to go with a 240mm/280mm system that'd be a bit different beast entirely but I'd only recommend that if you wanted to get more in to overclocking your system. The Nzxt X61 would help compliment your LED setup on the MSI motherboard. Corsair also offers line up of LED systems but the iLink software is dodgy.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835146042

I'd throw a 1Tb drive in there, since you're editing video you'll likely need more storage than the SSD can provide.
http://www.newegg.com/Product/Product.aspx?Item=N82E16822236339&cm_re=1TB_HDD-_-22-236-339-_-Product

Your motherboard is only a month old so reviews are thin on the ground but it seems solid, but it does mean you'd have to be a first gen user. Its the cheapest LED motherboard tho so if you're going for that look it sounds like a good deal. Otherwise I'd look at the Asus Pro Gaming or Gigabyte Gaming 5
http://www.newegg.com/Product/Product.aspx?Item=N82E16813132567&cm_re=Asus_Pro_Gaming-_-13-132-567-_-Product
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128836&cm_re=Gigabyte_Gaming_5-_-13-128-836-_-Product


Finally, consider a i7. The multithreading will be a huge help if you do a lot of video editing.
http://www.newegg.com/Product/Product.aspx?Item=N82E16819117559&cm_re=i7-6700k-_-19-117-559-_-Product

if you can hold off. wait till after the paper launch of pascal gpu on first week of april. then in june the desktop parts will be dropping for pascal.

Never a bad thing to have too much power. While a 750w is more than needed, its better to have a higher ceiling so theres less stress put on the parts for a longer life span and better efficiency in the PSU.

there's a limit to the efficiency. the 'sweet spot' is between 50% and 80% of rated power for maximum efficiency.

True, but at load the OP's setup would start hitting about 60% of the rated power of a 550w. A 750w would bring that down and allow for future expansion without sacrificing efficiency. So if a quality 750w is coming in at roughly the same price as a quality 550w due to a sale, there's no reason not to go for the 750w. Now if we were talking a huge price difference than sure a 550w would be a much better option than the 750w but that wasn't the case when I put those prices together.

since the listed build is about 345W, 50% would be 690W. However, if you plan to overclock, you might push up to near 400W, which would be above the 50% threshold for the 750W (375W would be 50%), making it worth using.

Think I may have been screwing up my math on that one then... long day at work and all. However is there any downside to going with a higher watt PSU if the pricing is the same?

slightly less power efficency. in this case, probly no real long term downside. a few cents a month higher electric bills at most.