Build feedback please
This machine will be used for two main functions.   When it is not cracking hashes it will be hosting a pentest lab VMs (between 20 and 40 VMs), this is why the CPU/RAM is the way it is.  Im curious if there is a known issue with any of this hardware or if there is a better combo of GPU.  Thanks for having a look.

CPU: Intel - Core i9-7900X 3.3GHz 10-Core Processor 
CPU Cooler: Corsair - H105 73.0 CFM Liquid CPU Cooler 
Motherboard: ASRock - X299 Taichi ATX LGA2066 Motherboard
Memory: G.Skill - TridentZ 64Gb (4X16GB) DDR4 3600 F4-3600C17Q-64GTZ
Storage: Samsung - 850 Pro Series 1TB 2.5" Solid State Drive
Storage: Samsung - 850 Pro Series 1TB 2.5" Solid State Drive 
Video Card: EVGA - GeForce GTX 1080 (Founders Edition) 8GB Video Card
Video Card: EVGA - GeForce GTX 1080 (Founders Edition) 8GB Video Card
Video Card: EVGA - GeForce GTX 1080 (Founders Edition) 8GB Video Card
Case: NZXT - Source 530 ATX Full Tower Case 
Power Supply: EVGA - SuperNOVA T2 1600W 80+ Titanium Certified Fully-Modular ATX Power Supply
Maybe I'm crazy, but wouldnt you prefer more cores and ram than that for a VM lab? You can easily build a cheaper system with more cores and more RAM(also ECC RAM at correct speeds, not the fastest overclocked gamer ram you can find online). Just look at some of the common dual xeon boards and grab some v1/v2 xeons on ebay for super cheap. If you really want latest and greatest, v3/v4 really aren't that much more and you'll end up better off overall.

As for GPUs, you won't be able to buy 3 GTX 1080 Founders most likely. They are incredibly scarce since they are already out of production. Really just try to grab any blower fan styled cards at this point. Do realize that if you plan to run those VMs under a hypervisor and not in something like VMware, you will need to make sure your hypervisor can pass the GPUs through to whatever system you want to run hashcat on.
Unfortunately its for work so ebay is right out. More cores and more RAM are always good. I tried to mix up some dual xeons but kept ending up more expensive, Ill try again.  The RAM was selected for MOBO compatability and didnt cost much more than the slower but still ridiculously fast RAM (and it was in stock).  ECC isnt high on the list since none of this supports production workloads, data loss would just be an inconvenience. 

I agree on GPU availability concerns and Im prepared to tone those down a bit if I have to.

We wont be running hashcat in a VM, it will run on the host with the VMs all shutdown, but that was a good callout, I wasnt clear about that in my post.
Ah ok, that all makes sense. I'd still be careful with the higher speed RAM dimms, I've not heard good things about their stability, even when used "properly" with the correct XMP profiles. You might be fine with them, I've not personally used them so it's hard to say how true those claims are.

New Xeon machines run a premium, so if used is off the table, you may be stuck with consumer/pro-sumer targeted hardware like the LGA2066 platform. Be aware, there are limitations that you wouldnt normally run into due to this like the limitations on what SSDs you can use when using features such as VROC(Virtual RAID).

As for GPUs, you could always go with something like these:

They may not be as nice as the FE cards, but at least the fan style is still the same so you will still get roughly the same cooling performance as the FE cards. The main thing to make sure of is that your case has proper airflow to feed fresh air to the cards. The blower fans take in case air and exhaust it all out the back of the case, which avoids recycling hot air but ends up requiring a bit more case pressure/flow than you might expect to keep them running effectively and well fed with fresh/cool air.
Ok so blower design cards of any flavor will still get me where Im going.  Didnt know about the case pressure issue, Ill toss in a few extra fans to keep that up. Thank you for the info, it has been quite helpful.
Yup, no problem. That seems to be one of the things a lot of people overlook when building a box full of blower cards. They end up with poor case inflow and an overall negative pressure. Then their cards have to keep ramping up to try and cope with the lack of fresh air. You want to at least balance the air inflow vs outflow, and maybe lean a bit towards the inflow so you end up with an overall slightly positive pressure in the case. This will keep the cards fed with fresh air and can also help to keep dust and stuff out, assuming your intakes are all filtered.
The new GTX 1070 Ti will be available in FE version and might have anyway a better price/preformance ratio.