New built, 4GPU extensible to 6
Hi Forum,
I am building a rig for password cracking mostly NTLM and WPA and I would greatly appreciate some help. I spent some time reading previous posts in the hardware section and I mostly want to make sure that before I got ahead and spend over 6K on a built that I didn't miss anything. 

Below is my list for hardware

PSU : Evga SuperNOVA 1600 G2 - Power supply (internal) - 80 PLUS Gold - AC 115-240 V - 1600 Watt
GPU : Evga EVGA GeForce GTX 1080 Ti SC2 GAMING, 11G-P4-6593-KR, 11GB GDDR5X,
MB : ASUS X99-E-10G WS - Motherboard - SSI CEB - LGA2011-v3 Socket - X99 - USB 3.0, USB 3.1, USB-C - 2 x 10 Gigabit LAN
Memory : Corsair Memory Vengeance LPX - DDR4 - 64 GB: 4 x 16 GB - DIMM 288-pin - 2400 MHz / PC4-19200 - CL14 - 1.2 V - unbuffered - non-ECC
CPU : Intel Core i7-7740X X-Series 4.30GHz Quad-Core 8 threads 8MB cache LGA 2066 Box Processor
Case : Hydra II 8 GPU 6U Server Mining Rig Case, Dual PSU Ready
Fan : Hydra 120mm 4200rpm High Speed Fan for GPU Mining Rig Servers, 3 Pack
PCIE Ext : ThermalTake TT Premium PCI-E 3.0 Extender - PCI Express x16 cable - 164 pin PCI Express (M) to 164 pin PCI Express (F) - 2 ft - black (AC-050-CO1OTN-C1)
HD : Samsung 860 EVO MZ-76E500E - Solid state drive - encrypted - 500 GB - internal - 2.5" - SATA 6Gb/s - buffer: 512 MB - 256-bit AES - TCG Opal Encryption 2.0
CPU Fan : Cooler Master GeminII S524 Ver.2 - Processor cooler

I understand my current PSU is not enough butthe plan is to add a second one when we move to 6GPU.

Thanks in advance!
My biggest recommendation would be to reevaluate your GPU choice. You want a blower style card like the 1080 FE's. 

The cards you have listed will exhaust their hot air INTO the case and onto the video card below it. This will cause severe heat issues in a multiple GPU scenario.

Also consider your ram. In a previous post, the hashcat experts here recommended a bare minimum of 1gb of system ram per 1gb of total vram. If you go up to 6 1080tis, that would be 66gb of vram. Based on this, I would just jump for 128gb of ram. Wordlists are also preloaded into ram so more helps.
Thanks MackWage. Very useful.