Found this -
Actual SLI Fix that Works, Tested on x2 Maxwell GTX970 in 4K, Windows 10 Pro, 64Bit.
Please see screenshot for FPS Gain.
Method #1 (Maxwell)
SLI compatibility bits (DX1x): 0x080200F5 (Max Payne 3)
Number of GPUS to use in SLI rendering Mode: Choose how many GPUs you have in your system
NVIDIA Predefined number of GPUs to use on SLI rendering mode in DirectX10: Choose how many GPUs you have in your system
NVIDIA Predefined SLI mode on DirectX 10: SLI_PREDEFINED_MODE_DX10_FORCE_AFR2
Method #2 (Maxwell)
Out friend here user named 'hide291', mentioned an alternative method for Nvidia Maxwell GPUs (I can confirm that it works).
Open up Nvidia Inspector, Open Fallout 4 Profile, use the button to Reset it to Nvidia defaults and change just one setting:
SLI compatibility bits (DX1x): 0x080000F5 (Killing Floor 2, Catzilla, Dragon Age 2)
Use something like Frap to see FPS and compare which method works best for you.
Method #3 (Pre-Maxwell)
Its been reported that this method works for some people with Kepler Generation cards (600 Series), user 'Johnsenpai' says that it works on his SLI670, but that also my first method works a little better.
This is the one that fakes SLI on Maxwell, if you enable nvidia SLI indicator and enable this method on Maxwell it will look like both cards work but if you compare FPS to single card mode, it wont be any better.
Go to NVIDIA Control Panel and change SLI Rendering Mode to Force Alternate Frame Rendering 2
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Video of it also.
https://www.youtube.com/watch?v=hE-73NmcW8I
