Current xorg.conf for a 3x 1080p monitor side-by-side setup (with the left most 90^o rotated)

xorg.conf

# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 364.15  (mockbuild@)  Fri Apr  8 12:50:17 CEST 2016

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
EndSection

Section "Files"
    FontPath        "/usr/share/fonts/default/Type1"
    ModulePath      "/usr/lib64/nvidia/xorg"
    ModulePath      "/usr/lib64/xorg/modules"
EndSection

Section "InputDevice"
    # generated from default
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "auto"
    Option         "Device" "/dev/input/mice"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"
    # generated from default
    Identifier     "Keyboard0"
    Driver         "keyboard"
EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "DELL S2415H"
    HorizSync       30.0 - 83.0
    VertRefresh     56.0 - 76.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 660"
#    Option         "UseEdidDpi" "False"
#    Option         "ColorSpace" "RGB"
#    Option         "ColorRange" "Full"
#    Option         "DPI" "96 x 96"
#    Option         "DRI" "3"
#    Option         "FlatPanelProperties" "Dithering = Disabled"
#    Option         "UseEDIDFreqs" "False"
    Option         "NoLogo" "True"
#    Option         "ExactModeTimingsDVI" "True"
#    Option         "ModeValidation" "NoVesaModes, NoXServerModes, NoVertRefreshCheck, NoEdidModes, NoHorizSyncCheck, NoMaxPClkCheck, NoEdidMaxPClkCheck, NoExtendedGpuCapabilitiesCheck, AllowNonEdidModes, NoEdidHDMI2Check"
#    Option         "RenderAccel" "true"
#    Option         "UseEvents" "false"
#    Option         "TripleBuffer" "1"
#    Option         "DamageEvents" "1"
#    Option         "BackingStore" "1"
#    Option         "PixmapCacheSize" "70000"
#    Option         "OnDemandVBlankInterrupts" "true"
#    Option         "IgnoreEDIDChecksum" "DFP"
    #Option         "CustomEDID" "DFP:/lib/firmware/edid/dell_edid.bin"
    #Option         "UseEDID" "true"
    #Option         "ConnectedMonitor" "DFP-4.2,DFP-4.1.1,DFP-4.1.2,DFP-4,DFP-0,DFP-1,DFP-2,DFP-3"
    #Option         "ConnectedMonitor" "DFP-4.2,DFP-4.1.1,DFP-4.1.2,DFP-4"
    #Option         "UseDisplayDevice" "DFP"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    #Option         "nvidiaXineramaInfoOrder" "DFP"
    Option         "metamodes" "DVI-D-0: nvidia-auto-select +1080+420 { ForceFullCompositionPipeline = On }, HDMI-0: nvidia-auto-select +3000+400 { ForceFullCompositionPipeline = On }, DP-0: nvidia-auto-select +0+0 { ForceFullCompositionPipeline = On, rotation=left}"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Section "ServerFlags"
    Option "IgnoreABI" "True"
EndSection

Section "Module"
    Disable "glamoregl"
EndSection