Nvidia control panel settings->
Ambient Occlusion - Off
Anistropic filtering - User's choice start low first
Antialiasing FXAA - Off
Antialiasing Gamma Correction - Global (On)
Antialiasing mode - Application Controlled
Antialiasing Setting - Application Controlled
Antialiasing Transparency - Off
CUDA - GPU - Global (All)
Maximum Pre-Rendered Frames - Use 3d Application Setting
Multi-Display/mixed-GPU Acceleration - Single Display Performance Mode
Power Management - Prefer Maximum Performance
Texture Filtering Anisotropic Sample Opti... - Off
Texture Filtering Negative LOD Bias - Clamp
Texture Filtering Quality - Quality
Texture Filtering Trilinear Optimization - On
Threaded Optimization - Auto
Triple Buffering - Off
Texture Filtering Anisotropic filter optimiz... - Off
Vertical Sync - Use 3d Application Setting
Now find your D3prefs.ini file in your User -> My Documents -> Diablo 3
Right click -> edit
Find HardwareClass "#" Change # to 1 and Save/Exit
If you are having crashing problems as well and you are using windows 7 or later.
Find your Diablo3.exe -> right click -> properties -> compatibility tab
Check Run this program in compatibility mode for: Select Windows 7 in drop-down Save/Exit
Whenever you run Diablo 3 instead of double clicking the icon right click and run as Administrator.
In game settings
In graphics tab uncheck every box EXCEPT V-Sync
Set all drop-down menu graphics options to lowest values. Increase as FPS allows.
Goodluck! Hope to see you in game.