Building new gaming pc with ultrawide monitor

Hello everyone

I need you to do your magic, and help me out on deciding on components for my new build.
First off , english is not my first language so forgive me if i make typos.

Now to brass tax:
My goal is to build PC able to play most games on Acer Predator X34 3440x1440, mainly shooters( Battlefield 3,4,1, Fallout4, Withcer 3, you get the idea)
and RPG-s.( Building it to play Mass Effect Andromeda)

ATM i have this PC:

Processor: HexaCore Intel Core i7 970, 3366 MHz (25 x 135)
Cooler: Zalman 9900
Memory: 8GB Corsair Dominator CM3X2G1600C8D
Graphic card: Nvidia GTX970 Gigabyte windforce x3
Motherboard: Gigabyte X58A-UD5 v2
Power Supply: Corsair 1200w 80+bronze
SSD: INTEL SSDSA2M120G2GC 120 GB
HDD: WDC WD5000AADS-00M2B0 465 GB
Case: Coolermaster HAF X
Monitor: Samsung syncmaster xl2370

First question would be , should I upgrade, and if yes, what parts (besides graphic card and monitor obviously)?
If i go with upgrade, do you think another GTX970 in SLI would do the trick, or something else entirely? For example if you tell me that my PC is still ok i just need two GTX1070 in SLI or something-

If I had to go with new build I could not use any parts from previous PC, because i would sell it to my friend, and fund would go toward new build.

Another note on budget, its not limitless, and it is to some concern, but if you advised me on something that is more expensive, for sake of performance, and quality i would go with it.

Below i will list components i wish to buy, and my thoughts on them, so you can advise.
Also I will links to sites that are availble in my country: Croatia

Processor: i7 6800k or i76700k

I chose this over i7 6700k because of 2 more core,and since I allready have 6core, and it would seem like downgrade,I also plan to do streaming,and some light video editing (montages and such),but as I will say many times if you have strong point, i will consider.

Motherboard: ASRock X99 Extreme4, s2011-3 or ASUS ROG Strix X99 Gaming, s2011-3
Now this is tricky one, i looked on Newegg and most user reviews, are split between either great (5star) or bad (1star) which depending on product gives 3 or 4 stars. And that is not missing features, or something meaningless, but its total failure eg. it needs to be returned. On the other hand most of the 1511 motherboards have 5 stars rating.
My question is are those concerns legit, and if so would you advise to go for 1511 socket,and 4
cores (i know there are no 6 cores), or stick with 2011-3 and 6 core.Having durability in mind.and longevity of build itself.

Memory:Kingston Hyper X Savage DDR4 16GB (2x8GB) PC4-19200 2400MHz
It was one compatible with this mobo, but if you think there are better ones, or maybe 32GB suggest away.

Graphic card: ASUS ROG STRIX-GTX1080-O8G-GAMING or MSI GTX 1080 GAMING X
I suspect Asus is a bit better, but i will follow your advice, its not that big of a diference budget wise.

SSD: I allready have Samsung 850 EVO MZ-75E250b-EU 250GB
I got it as a great deal, so I went for it.

HDD: 1TB WD Black

I dont need bigger, but it had some good reviews, and it was available, also if you have other suggestions i will gladly listen.

Power supply : EVGA SuperNOVA 750 80+gold

I supose my 1200 w Corsair, was a bit overkill, since I did not plan to go SLI, but i think this is will be enough.

Cooler and case:
Cooler: Noctua nh-d15
I plan to do mild overclock out of the box,nothing much just to see how it goes.

Case: Cooler Master MasterCase Pro 5 or Fractal Design Define R5

Feel free to suggest something else, along those price ranges, because it is a steep price curve for full towers. But again if you know some that are affordable with quality in mind I am open to suggestions.For example something that has great airflow, or important in some other way.

Monitor: Acer Predator x34 or Asus ROG 34 pg348

If I understand correctly, these are only two with this resolution(3440x1440) , gsync, 100Hz (overcloced), to my knowledge, i dont need curve, so if you have any cheaper alternatives, i will hear them out.Or something else entirely. I chose 34, because they are same height , as my current monitor, but with extra space on the sides,i compared smaller ones and they seemed to low.

Places where i will be getting most parts:
http://www.adm.hr/

https://www.links.hr/hr/komponente-05

If you have trouble navigating in Croatian websites, just pick it on Newegg or Pcpartpicker , and I will try to find it here.

Conclusion: I would like to make build , that is somwheat futureproof, and to be able to play on ultrawide, at this resolutions, since its close to 4k, but with benefits of Gsync, higher refresh rates.
I dont care much for lights and glowing case, but i need dependability and sturdines for years to come. I am aware i will need to change graphic card in 2 years or so, but I did it with current PC, it had GTX580 when i bought it , and it needed to be upgraded. I am planing to spend A LOT on this, so any saves are more than welcome, but not at the expense of quality.
Let me explain:
for example, take any motherboard you want ,if you started talking too much about PCIe lanes and such you would lost me, because im not proficient enough, what i would like to get is this:
Hey this motherbord will do overclocking nicely, it has quality componenets and features and will last untill new upgrade, im for it. It does not need to be pretty or red and black,or have lights or any of that stuff.

Sorry for the long post, but I wanted to give you as much detail, and my concerns as possible.
And if anyone takes time to answer, I will be very gratefull, and to best and detailed answer i say : if you visit Croatia, beer is on me!
Thnx in advance
Kind regards.