Is this enough for 15 boxing

[MiRai]

Okey I changed my system and will buy the following:

Cpu: i7-5280k 6x 4.5 GHz oc
Gpu: 2x 4096MB Gainward GeForce GTX 970 Phantom Aktiv PCIe 3.0 x16
Ram: 32gb 1600mhz // maybe 2666 Mhz because my mainboard needs ddr4

resolution 1600x900

You seem pretty confident in that 4.5GHz overclock. I wouldn't factor that in until you're sure it's stable. Other than that, I assume the machine would work fine at the medium-ish resolution, but your GPUs are not going to both run in 16x mode because the 5820K (there is no 5280K) is limited to 28 PCIe lanes. With that said, I have absolutely no idea if this is going to affect you or not.

[Skow]

You seem pretty confident in that 4.5GHz overclock. I wouldn't factor that in until you're sure it's stable. Other than that, I assume the machine would work fine at the medium-ish resolution, but your GPUs are not going to both run in 16x mode because the 5820K (there is no 5280K) is limited to 28 PCIe lanes. With that said, I have absolutely no idea if this is going to affect you or not.

So here is now my last built:

Hdd: 1TB 64mb cache Western Digital
SSD: Crucial 128GB 6GB/s
Powersup: be quiet! 750W
Cpu Cooler: be quiet! dark rock advanced c1
Case: Corsair 350D
Cpu: i7 4590k 6x 3.3 ghz (hopefully oc to 3.8 - 3GHz)
ram: Vengeance & ballistix 32GB 1600mhz ddr3
mainboard: asrock x79 extreme9 intel x79 so.2011
gpu: 1x gtx 980 or 2x gainward gtx 970 4gb phantom / should I go for 1 980 or 2 970 ?

[multiboxduck]

Are you upgrading up from? I'm curious where you're coming from with regards to #of boxes or system(s), surely previous multiboxing experience would provide alot of guidance for you?