So I will be running 2x r9 295x2 in crossfire, ASUS Crosshair V Formula-Z AM3+ AMD 990FX SATA 6Gb/s USB 3.0 ATX AMD Motherboar

I wouldn't do that with am3+. I'd look to x99 for a rediculous setup like that. You would probably be better off with a pair of fury x's or a pair of 980tis that 3rd and forth gpu is not going to amount to much. Depending on resolution you will probably run out of vram before you even touch the surplus core power. You will need a beastly and high quality psu.

My friend just built a x99 (5820k) with 980ti SLi and it rocks @ 4k res.

If you need maximum RAM then 2 titan x's (although it is def not worth it imo)
 
Yeah Z170 or x99 + 980tis would be my choice, for the money x99 and 980ti SLi

Here is the build I made for my buddy + 1 more 980ti

https://pcpartpicker.com/user/jjb8675309/saved/#view=PQ4WGX

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i7-5820K 3.3GHz 6-Core Processor ($374.99 @ Newegg)
CPU Cooler: Corsair H100i 77.0 CFM Liquid CPU Cooler ($149.99 @ Newegg)
Motherboard: ASRock X99 Extreme4 ATX LGA2011-3 Motherboard ($139.99 @ Newegg)
Memory: G.Skill Ripjaws Series 32GB (4 x 8GB) DDR4-2666 Memory ($214.99 @ Newegg)
Storage: Samsung 850 Pro Series 256GB 2.5" Solid State Drive ($129.89 @ OutletPC)
Storage: Samsung 850 EVO-Series 500GB 2.5" Solid State Drive ($147.99 @ Newegg)
Video Card: MSI GeForce GTX 980 Ti 6GB Video Card ($639.99 @ Newegg)
Case: NZXT Phantom 820 (White) ATX Full Tower Case ($191.99 @ SuperBiiz)
Power Supply: EVGA SuperNOVA 1000 P2 1000W 80+ Platinum Certified Fully-Modular ATX Power Supply ($181.99 @ SuperBiiz)
Operating System: Microsoft Windows 8.1 Pro (32/64-bit) ($202.98 @ Newegg)
Total: $2359.79
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-11-24 15:33 EST-0500

For the money id swap out windows 8.1 pro for windows 10 pro (non OEM) same price and less hassle to upgrade.

The above build is overkill in many ways but gives you an idea of what a system like the one your proposing could look like.

The Phantom 820 was an awesome case to build in. Made everything very easy to assemble.