My guess would be it's a power issue
 
F.Y.I just because you have a 1200w PSU doesn't mean it's not failing
 

If the physics test is crashing, I'd bet money on your CPU overclock being unstable.  Did you do any stability testing with it?  OCCT for a couple hours?  AIDA64?  Or......browse the internet and play a game or three?  Cause....the latter, does not make your CPU stable, and....the physics test WILL put enough pressure on it, to make it crash.

Assuming you're talking about the "physics test" in Firestrike?  Because the physics test in Firestrike, and all the others, btw...is ALL CPU.  Setting the 2nd card to "physx" or cpu to "physx" doesn't do a thing in 3D Mark tests, because it's not testing "physx", it's testing the CPUs ability to properly calculate physics.

As for the BSOD as soon as you enable SLI...have you tested each card individually, to make sure they don't have any problems?

Ok answering to the last query made me trouble shoot it one more time :)
Earlier the system did not boot up into windows after I put together the new build. It used to crash as soon as the sign in screen poped up. So I thought the GPUs are were not getting enough power so I connected 4 individual 8 and 6 pin rails directly from the PSU. Now I tried the 6+8 split rails and it's working fine... So I guess the issue was too much power going to the cards :)
Sorry guys I feel stupid. :'( #noob

creative4art

kwkrnu72
If the physics test is crashing, I'd bet money on your CPU overclock being unstable.  Did you do any stability testing with it?  OCCT for a couple hours?  AIDA64?  Or......browse the internet and play a game or three?  Cause....the latter, does not make your CPU stable, and....the physics test WILL put enough pressure on it, to make it crash.

I have done RealBench and other Benchmarks and it was all fine. The issue is present without OC even. 
 

kwkrnu72
Assuming you're talking about the "physics test" in Firestrike?  Because the physics test in Firestrike, and all the others, btw...is ALL CPU.  Setting the 2nd card to "physx" or cpu to "physx" doesn't do a thing in 3D Mark tests, because it's not testing "physx", it's testing the CPUs ability to properly calculate physics.

This is not true. By default NVidia sets second card to Physx. I tried setting it to CPU and it crashes... When I use Dedicate to Physx, the tests go fine all the way to the end. 
 

kwkrnu72
As for the BSOD as soon as you enable SLI...have you tested each card individually, to make sure they don't have any problems?

NO BSODs when I enable SLI. Only PC Shuts down when I do Physics Tests. The PC runs fine otherwise. 
 

Sajin
When you say with or without overclock are you talking about your gpu or cpu? Try running both the cpu & gpu at stock clocks and see what happens.

Yes I have tried stock without OC on both CPU and GPU. 

MrImSoGood
My guess would be it's a power issue
F.Y.I just because you have a 1200w PSU doesn't mean it's not failing

How come?? 1200W should have enough Juice right? I am even connecting 6 pin and 8pin connectors seperately instead of the 6+8 split ones from the PSU. Corsair Link should show the accurate power consumption right?  
 

Uh...physx doesn't have anything to do with the 3D Mark tests.  It's all physics, and all CPU.

Glad you got it figured out.

kwkrnu72
Something may have been overloading the PSU because of the way the cables were set up, but.....you're not going to get too much power to the GPU.  

 
Not sure what was the issue... but I have had all the CPU, ATX and PCIE cables go to the right place, and the peripherals to the Sata/Fans etc... I mean there is nothing else that could go wrong right? :/ 
So far its working fine with the 8+6 split cable as opposed to the individual 8 and 6 cables.