Well Chris21010's rig has been inspirational, but I'm not quite the artist / craftsman he is, so I'm trying figure out a more straight-forward multi-gpu machine I could build.  Simple, reliable, high bang for the buck and minimal use of a dremel are the initial design criteria.
 
Four GPU's on air would generate a lot of heat, so hydro seems the way to go.  Given the simple design goal plus the fact that I have zero liquid cooling experience, I'm thinking all AIO cooling.  The CPU must have 40 PCIe lanes and the motherboard must accommodate 4 double width graphics cards without modifying the cards or motherboard.  I'm not sure how to pick a case that would handle 5 AIO radiators attached to it somehow.
 
Here are the basics:
GPU - EVGA GeForce GTX 1070 FTW HYBRID GAMING x 4 - $489 each
MB - EVGA X99 FTW K - $250
CPU - Xeon E5-2620 V4 2.1(3.0) GHz 85W – 8 – Core – 40PCIe -  85W - $450 - 10 cores adds $300 - E5-2630 V4
SSD - SAMSUNG 850 EVO M.2 500GB - no power or data cables is the motivation behind going M.2 - $160
PSU - EVGA SuperNOVA 1200 P2 80+ PLATINUM 1200W (a 1000W might do, but headroom is never bad) - $230
CPU Cooler - CORSAIR Hydro Series H60 - $60
RAM - 32GB of something compatible, and won't interfere with anything in the case - $200
Case - ??
 
Clearly open to overall suggestions, but here are the open items I'm thinking about:
CPU - Want to crunch with it, so total compute power matters.  When comparing processors, can all cores go Turbo at the same time?  The i7-6800K only supports 28 PCIe lanes, so I think it's out of the running.
MB - Can save ~$80 by going with a GigaByte GA-X99-UD3P, but I don't want the MB to be the weak link.  Is the EVGA X99 FTW K the right MB?
Case - The highest end case I've ever bought is $100 Antec Sonata back in the day.  So I'm starting from scratch on this one.  Any ideas?
 
Figured this just might be something fun to toss around.

you can not run 4GPU and m.2 on that mobo. when you put something in that m.2 slot the bottom pci-e is disabled.

ya m.2 either shares or replaces pci-e lanes. so no matter the motherboard if you are going to try for a 4 GPU setup you'll want to look into a standard SSD.

hybrids will be fine for a 4 card setup as the GPU is the primary source of heat. not to mention that EVGA hybrids also cover the VRAM so they are not strictly air cooled.

bcavnaugh

Chris21010
hybrids will be fine for a 4 card setup as the GPU is the primary source of heat. not to mention that EVGA hybrids also cover the VRAM so they are not strictly air cooled.

Yes the FTW Model has an added Copper Plate for the VRAM, but not the Non-FTW Models.

Great to know.  I didn't know there was a cooling difference.
 
Where did you read that the FTW Hybrid has an added copper plate?  I've been trying to figure out the difference between the FTW and regular 1070 hybrid, and the eVGA spec sheets are identical.

Will a hybrid 1070 even fit in the bottom slot of the EVGA X99 FTW K?  It looks like there are numerous headers, etc. that would be covered up.
 

I think going with five AIO coolers (4 gpu plus 1 cpu) would be redonkulous. That's now five weak links, making it much, much more likely that you will see a failure of some sort in the future. Water cooling isn't that hard, and there are plenty of people here who can help make this very simple for you. I'd suggest that you just go full-on water cooling and keep your points of failure to a minimum. One good, high-quality pump will be much more reliable than five of whatever crapco pumps they build into the AIO coolers.
 
AIO tubing is typically quite short. You're going to struggle to mount five AIO coolers close enough to all those cards and your cpu. Not to mention it's going to be a veritable rat's nest in there, a jungle of ugly black tubing making your machine look like crap and impeding internal airflow.
 
Seriously, start asking questions about water cooling. Start reading about it. It's very easy to do. It's a far better solution for what you're wanting to do than going with a dog's breakfast of crappy AIO coolers.
 
Also, using the cpu to fold isn't really worth it. I've been folding with 6 or my 8 cores on my i7 6900, but it's only adding like 60k ppd or so to my potential output (1/15 of what my 1080 does) for about half the power draw. You'll also need some cpu cores free to support the gpu folding on four cards.

Yeah, go with a standard SATA SSD - there would be no measurable benefit on this machine from going m.2, and like the others have said, you won't lose a PCI-E slot.

sethleigh
I think going with five AIO coolers (4 gpu plus 1 cpu) would be redonkulous. That's now five weak links ... One good, high-quality pump will be much more reliable than five of whatever crapco pumps they build into the AIO coolers.
 
... Also, using the cpu to fold isn't really worth it.

Thanks.  I figured this might come up and I've never seriously looked into a full hydro solution.  I'll do a bit of research.  My guess is, it will get pretty expensive with $100+ waterblocks per GPU.  Might just have to research this a bit more.  How often do AIO pumps fail?  More often than fans?
 
Also, don't plan to use the CPU to fold, but I'll crunch with it.
 
Great comments.  Thanks again.

This case can hold 5 or more AIO Cooler Units. Core X9 E-ATX Cube Chassis

 
You could install 4 Hybrid Rads on top and even a H100i v2 on top for the CPU.
 
 
Lots of room in this case

a 240mm or 280mm radiator is plenty for cpu's under 100W

Photo of a system with 3 AIO Titan X's in it.  Definitely a lot of tubes...
http://forums.evga.com/FindPost/2320877
 

Super old thread, but wanted to say, I did end up building up a rig with the potential of 4 1070 hybrids.  I only ended up with 2 so far.  Currently debating a 1080 hybrid or a third 1070 depending on funding.
 
Build so far:
GPU - EVGA GeForce GTX 1070 FTW HYBRID GAMING x 2
MB - EVGA X99 FTW K
CPU - I7-6850 - 6 Core – 40PCIe -  3.6 GHz (OC'ed to 4.0GHz)
PSU - EVGA SuperNOVA 1000 G2 80+
CPU Cooler - Coolermaster 212 EVO
Case - CoolerMaster MasterCase 5 Pro
 
I knew the case was a close fit for the Motherboard, but I just went for it figuring I replace an old case with it and buy a new bigger case if I needed to.  The motherboard did fit, but there is no room for the 4th 1070.  So, I have room for one more GPU.
 

 

bcavnaugh
How are you going to Mount 4 GTX 1070 Hybrids cards?

Need a new case for 4.  I had hoped this one would be big enough, but it's barely not for the physical cards.  I believe the coolers would fit mounting one on the back of the case and one on the front.
 
However, when I get there I will buy a bigger case.

You could interpose a 6162-KR in between them. And keep the case.