I have this: http://www.newegg.com/Pro..._-20-721-108-_-Product

So memtest first time failed, second time you tested each stick in slot 1 and came back fine. So the ram is fine but its possible one of the other DIMM slots is messing up. Try removing all ram except for slot 1 and do benchmarks again just to see. If you need at least 2 stick do a test on the second slot for an hour and try with two stick. If results are the same we can rule that out. The reason iam still looking at hardware is because the black screen during the memtest.  The fact your pc is freezing isnt a good sign either. Another thing i would check is your power supply.  Grab either a new one that you can bring back or take your wifes psu out and just disconnected yours and just roughly connected the known good one and run quick test again.
 
You can do the fresh windows install test by using a spare hard drive and install on that and just install only things you need to test. That way if there is no change you can just put your old one back in no extra work required.
 
Now your issue is clearly strange, everything looks working but something is wrong. I seen weird unexplained issues from computers that came from the power supply not giving consistent voltage so I would not rule it out as possible. That being said if the DIMM slots are for sure working, the PSU is for sure working correctly I would again believe its a software issue but still doesnt explain how the memtest failed. Interesting problem and i hope you get it figured out.
 
EDIT: Someone pointed out high gpu temps while testing, why dont you try removing the side of your pc and redoing the test again just to see if its a case air flow issue as well. I would do that first.

Hi minty fruits
Make sure in Bios PCIEX8_2 is on Gen3 and the other PCIEX16/X8_1 is on auto.
 
Try taking all your devices out of the pcie slots and pci slots and just leave the 1080 gtx in slot 2.  Try it see if it gets better fps if the above doesn't work. If you want to take the 1080 gtx out and push it back all the way in. Slide the lock to lock the gpu.
If that works then we have a Hardware conflict problem.
 

In your Nvidia control panel you have the Power Management mode to maximum performance?
Also in windows power settings you have it on High Performance profle?
 

Alright download driver booster. http://www.iobit.com/en/driver-booster.php
Install it and run it. see if it finds any new updates. If it does install them. After everything is installed restart pc and try the benchmark or a game to test.
 

Hi download this user benchmark http://cpu.userbenchmark.com/Software 
Run it. After you run it go here http://cpu.userbenchmark.com/ click compare. Add everything you have in your pc there. Then compare that to your system to see how far your system is off.

Just to clarify some things mintyfruits,
 
Before you installed your new GTX 1080 your PC was in good working order and with zero problems yes? and playing games with your GTX 980ti was great also with zero problems yes?
 
if this is correct then why are you now testing things in your PC that previously had no problems?
 
 
From my short testing of the GTX 1080 it is not the power house of a GPU as some might think it is and especially if you are upgrading from a previous high end card, i'm upgrading from a GTX 970 SSC and yes I can now max games out and have playable framerates but some games will not give constant 60+ fps at 1920x1080 144Hz, at least this is what I have experienced. Most review sites show that once you go 2560x1440 and above then expect some games to tax heavily one GTX 1080. In my honest opinion once you go 2560x1440 and high refreshrates you need at least 2 way SLI to cope with some of the recent games, that's not my opinion, this is based on others reviews, and you can clearly see the stats. Fully maxing out The Rise of the Tomb Raider I can bring the GTX 1080 to an average of 45-50 fps at 1920x1080 144Hz [VSYNC OFF ]
 
 
The GTX 1080 FE is a really nice design, thermals and noise are a good in my PC and I never had any expectations of something other in my minds eye, NVIDIA engineers did really well imho, I see this GPU as a really good upgrade from my GTX 970 SSC even for 1920x1080 144Hz and truely maxed out games.

VeRsUaL
Kenvray
 
On a 1080 gtx your fps on Rise of the Tomb Raider at 1920x1080 should be around 131 fps on avg and at
2560x1440 around 90 fps on avg.
 
Here is the link http://www.guru3d.com/articles-pages/nvidia-geforce-gtx-1080-review,13.html
 
Looks like you have some problems also with your card.

They are not maxing out tomb raider plus they are using 60Hz panels/monitors, some reviewers choose the graphics presets in the games menu, some games have custom settings with more settings like NVIDIA gameworks. Hexus.net did a review of the GTX 1080 Founders Edition but they too only chose certain in game presets and on 60Hz monitors.

VeRsUaL
Here is a video to compare https://www.youtube.com/watch?v=B13m6DDZny4
Did you watch the video? They max out everything and they use 144 Hz. Set it up like they do and see what you get and compare.

Yeah I watched that video, that person never chose DirectX 12. If I use the same settings as that person I get maximum of 145 fps, average 90-100 fps and this was with DirectX 12 enabled. If I choose SSAA 4x Anti-Aliasing  I average 45-50 fps, I am talking about maxing a game engine out, not everyone is maxing their game settings as that person in the gameplay video was not. At the end of the day the GTX 1080 FE is a really really great card and gamers can choose certain graphics settings that they prefer, I'm talking about maximum graphics settings and I mean every possible setting as high as it will go, I don't always use every graphic setting, it's just to see how far i can push the GTX 1080 before the framerates get too low and the game becomes choppy or lags, that is all. This is not to diss the GTX 1080, it is a very well designed GPU from NVIDIA, I am very very pleased I got one, but I am upgrading from the GTX 970 SSC which was also a very well designed GPU by EVGA.

The scores you are getting at not close to what they should be, Try a clean windows install and go from there

If a clean install of windows doesn't fix your original problem/freezing problem I'd suggest replacing your motherboard.

Sajin
If a clean install of windows doesn't fix your original problem/freezing problem I'd suggest replacing your motherboard.

+1
 
Mintyfruits, as I posted earlier on this page:
 
You tested each stick of RAM, one at a time, in slot one and they all passed? 
 
And when you originally tested the RAM, all sticks were installed, and you came back to a blank screen? If so, RMA that motherboard because it has a bad RAM slot.

mintyfruits
If I have to go that route, could I get some motherboard suggestions?

http://www.newegg.com/Pro...x?Item=N82E16813128834

KEVRAY

mintyfruits
If I have to go that route, could I get some motherboard suggestions?

Why would you need to get another motherboard if you had no issues before you installed the GTX 1080? when I get the funds together I will be purchasing 16GB (8GB x2 dual channel) of RAM for my Maximus 8 Hero, I will follow Corsairs recommendations with the Maximus 8 Hero and start minimum of 2400MHz, Corsair don't recommend 16GB kits of 2133MHz RAM for the Maximus 8 hero, it's not even on their memory finder for 16GB kits with this motherboard.

The 1080 works fine in his wifes pc. The OP's rig also has multiple issues.

mintyfruits
Attempting a windows reinstall, however I keep getting an error. -_- this never ends.

 
What is the error?