Sajin
Since you're still freezing I would suggest testing your ram like I suggested back in post #12. You should also check your cpu by running the intel diagnostic tool.

+1
 
You might also want to scan your boot drive for errors. Right click on the boot drive -> properties -> tools -> check (if you are running Windows 10)
 
A reboot might be required for the drive to be fully scanned.

Intel Diagnostics:

double

mintyfruits
Intel Diagnostics:

Intel change Diagnostic Tool version, they removed some Not Supported and not used settings...
I was shocked before one year what happen with my CPU until I didn't found pictures from same software on same Processors generation as mine.
Now and my Pass all tests, no more Not Supported and similar... stuff.
 
Are you close to discover source of your problem or dead ends on all sides.
I could play with other systems until I discover culprits how long is necessary, but when my system is problematic I'm anxious and nervous and in depression and angry...
But it's much harder when someone explain you something over net and can't directly to look in all settings and what's happen after changing different things.

How long should the memtest run? It's been going for over an hour.

So this is normal, yeah?

The 3DMark Firestrike Physics score seems low for a Skylake i5 6600K

I would replace the mobo and buy ram from the QVL list on the manufacturer's website. For example, that mobo supports much better speeds ram and using an asus board they allow you to set the timings by selecting the memory profile in bios. Its stupid easy.
 
Besides that, I would make sure you have a decent SSD not a normal HD because they are terrible and probably can't keep up while gaming anymore.
 
Are you monitoring your system while gaming at all?
monitoring.JPG                 
Ignore the GT520 :( I sold both my old SLIed 660Ti Boosts 2 weeks ago, expecting the EVGA 1070 to be buyable today, silly me. But either way, if you running windows 7, gadgets can tell you a lot, if your running win 10 the resource monitor is also very helpful and with a little extra help you can run gadgets on 10 too. Look for what is capping out on your system and fix it. If nothing is capping then assume it is the newest hardware and RMA it.

Rise of the Tomb Raider is a really demanding game, been play testing, Direct X 12, maxed out graphics, SSAA x4, hairworks very high, every setting as high as it will go all effects enabled and VSYNC is off, the benchmark shows overall 62 fps but in game the framerate is up and down, minimum framerate 45, maximum framerate seen was 61 fps, but I average 45-50 fps, it looks great though. Also, Precision X OC on screen display does not work with my game, I used the Steam framerate counter. It is hardly suprising that at my settings and at 2560x1440 the framerate would be seriously low, I would need minimum of 2 way SLI at that resolution. Gameplay is not smooth at my framerates I will have to back down on some settings, this game eats the GTX 1080, but I suspect my GTX 1080 is throttling, In Tom Clancy's The Division I saw max temp of 85C.

@KEVRAY I hear you. But my concern comes from that I havent changed any settings since my 980 Ti and that was getting 60-70 FPS. Now on the 1080 it is getting 30-32.

Also, no idea on the memtest. I came back to the computer and it had stopped and was on a blank screen.

Nope. :( Got it from Step Up.

mintyfruits
Nope. :( Got it from Step Up.

Can you not step down?,
 
 
 
 
just joking

Do you have a spare hard drive to clean install windows onto? That would help rule out a lot of things. 
 
If so, reinstall onto a spare drive, install fire strike and see what it scores, then you can try out the games. 
 
 

Mint,
 
Did you disable the Intel integrated graphics that comes in the board? If not disable it.  Also in the near future, please invest on a 1000W PSU.  The reason for that you want to give breath room to the PSU when you keep adding hardware. 

Mint, 
 
Try uninstalling/reinstalling the Nvidia drivers again, but this time please BE SURE TO UNINSTALL THE VULCAN RUN TIME LIBRARIES also. I noticed in the control panel the Vulcan libraries where integrated in the Nvidia drivers of 4/2/16 and the Vulcan libraries are also updated with the drivers.  The order i usually follow when uninstalling drivers from Nvidia in control panel is as follow:
 
Vulcan Run Time Libraries
Nvidia 3D vision Controller Driver
Nvidia 3D Vision Driver
PhysX
Nvidia GeForce Experience
Nvidia HD Audio Drivers - restart if you have it, if not
Nvidia Graphics Drivers
 
restart in Safe Mode. go to the DDU App, choose clean but do not shutdown/restart. Go to the C:/ and look if there are any Nvidia folders, if they are delete them, then click on clean and restart, and proceed to install your drivers.
 
Please post the results.