2 questions about potential builds
I currently have a poweredge R900 (4 hexacores) I use with hashcat. I just saw the release of v3 which mixes CPU with GPU. Would it be dumb, or is it even possible, to put 2 GeForce GTX 1080 into this server to leverage the 24 CPU's and the GPUs?

Second if that is stupid I saw a post on a netspi forum with a setup looking like this.

Case 6 GPU Rackmount Server Case
ASRock Motherboard H81 PRO BTC
PCI-E 1X To 16X USB 3.0 Riser Card
XFX Black Edition R9 290
^ I would change to the 1080s[/url]
[url=http://www.newegg.com/Product/Product.aspx?Item=N82E16817139039]CORSAIR AX1200i 1200W

Dual PSU Adapter Cable
Intel Celeron G1820 Dual-Core (2.7GHz)

Is this a decent build on a budget? Would be around 3500 roughly.
This is Eric from NetSPI. I wouldn't use that guide to build a box anymore. It's outdated and was built off of what bitcoin miners were doing. You'll need enough memory to at least match what's on your cards and the processor should be anything better than a celeron. The risers are probably fine and the motherboard is ok. That case is really terrible because the fans are backwards and the only way to fix it is to move them around, but then you're blocking cables from the PSU. We figured that out too late which is unfortunate. It still cools, but is bad for reference cards.