This script works for me in everything up to 4.13 (so far)
Create a DefaultGameUserSettings.ini in your config folder and copy / paste the below script into it.
[ScalabilityGroups]
sg.ResolutionQuality=100
sg.ViewDistanceQuality=3
sg.AntiAliasingQuality=3
sg.ShadowQuality=3
sg.PostProcessQuality=3
sg.TextureQuality=3
sg.EffectsQuality=3
[/Script/Engine.GameUserSettings]
bUseVSync=False
ResolutionSizeX=1920
ResolutionSizeY=1080
LastUserConfirmedResolutionSizeX=1600
LastUserConfirmedResolutionSizeY=900
WindowPosX=-1
WindowPosY=-1
bUseDesktopResolutionForFullscreen=True
FullscreenMode=0
LastConfirmedFullscreenMode=0
Version=5